When Rey contacts the Jedi of the past, their voices can be heard. From Mace Windu and Qui-Gon Jinn, to Luke Skywalker and Obi-Wan Kenobi, to Kanan Jarrus and Ahsoka Tano.
One of the early scenes features a festival that happens once every 42 years. The original film was released in 1977, 42 years before Rise of Skywalker.
Original Trilogy
The Resistance flagship is a repaired Tantive IV.
At the Festival of the Ancestors on Pasaana, an Ithorian and a Snivvian, two species that made their debuts in the very first film of the saga can be seen attending the festivities in the background. The Ithorian is particularly noticeable when Lando shoots a stormtrooper to buy our heroes some time to get away from the First Order's patrols.
When Rey is scaling the wreckage of the Death Star II, she climbs up a platform that resembles the tractor beam control on the first Death Star.
Rey visits the abandoned Lars homestead on Tatooine and buries the two Skywalker lightsabers (Anakin's/Luke's and Leia's).
The Orbaks ridden by Jannah's people are essentially horses adorned with thick furs and tusks, which is a nod to how Mardji the elephant was dressed up to portray A New Hope's banthas.
When Kylo/Ben says 'Dad' and Han answers 'I know,' this is a call back to the iconic scene between him and Leia in Empire Strikes Back right before Han went into the carbonite freeze. He knows his son loves him.
Wedge Antilles is in the gunner's seat of the Millennium Falcon during the Battle of Exegol.
The Ewoks make an appearance during the victory celebration as does Cloud City on Bespin. For bonus points, the Ewoks are Wicket (with Warwick Davis reprising his role) and his son Pommet (played by Warwick Davis' real-life son Harrison.)
Palpatine opens the roof of his Sith chamber to show Rey the unfolding Final Battle in order to taunt her with her friends' impending defeat, like he did to Luke in Return of the Jedi.
Supplementary material confirms that the Resistance's Mon Calamari pilot is the son of Admiral Ackbar.
Like his grandfather before him, Ben Solo is redeemed on the Second Death Star - while Vader was redeemed by his son when the war machine was at the height of its power, Ben is redeemed by a vision of his father on the space station's ruins.
Luke lifts his X-Wing out of the waters of Ahch-To the same way that Yoda did on Dagobah all those years ago. For bonus points, the exact same piece of music plays while he does so.
Rey encounters a Dark-side reflection of herself, just as Luke did on Dagobah.
Palpatine throws Ben into a ravine, as payback for how the Skywalkers once threw him to his death.
Going back to the very first film in the series, Obi-Wan describes the lightsaber as a weapon that the Jedi use "only for defense, never for attack." Here, Rey proves the truth of that statement in the most spectacular way possible when she uses Luke and Leia's lightsabers to reflect Palpatine's force lightning back at him, melting the flesh off his bones in the process.
Before Luke shows Rey Leia’s lightsaber, he says “There’s something my sister would have wanted you to have”, called back to how when Obi-Wan gave Luke Anakin’s lightsaber, he said “Your father wanted you to have this when you were old enough.”
On Pasaana, Lando Calrissian wears a face-concealing helmet to disguise himself, like he did at Jabba's palace.
Rey learning she's a Palpatine echoes Luke learning he's Vader's son. Rey's parents being nobodies is as Metaphorically True as Vader killing Luke's father.
Prequel Trilogy
Rey, Finn, Poe and the droid hide in an astroid field on Ochi of Bestoon's ship after escaping Pasaana having actually landed on an asteroid - this is akin to Obi-Wan landing his starfighter on one in Attack of the Clones. Also, like Slave I also hiding in the asteroids and following him, the Knights of Ren do the same here.
A B1-Battle Droid can be seen in Babu Frik's workshop. It's visible even in the trailer.
The design of the Sith Trooper helmets is very similar to that of the Phase II clone trooper helmets.
The secret operation carried on Exegol for many years at Palpatine's behest, one which involves cloning, is reminiscent of what went down on Kamino.
Palpatine is ultimately defeated via Rey deflecting his own Force lightning back at him, similar to how Mace Windu did the same to him during their battle in Revenge of the Sith, but with a more positive outcome.
The resurrected Palpatine is wearing red robes under his black cloak, similar to those he wore in Revenge of the Sith when he fought Mace Windu and the other Jedi masters when they came to arrest him for treason.
The turning point for Kylo Ren's character is an intentional inversion of his grandfather's: whereas Anakin embraced the Dark Side after being left to die on a planet of fire, Ben turns to the light once and for all after being left badly injured on a planet of water.
Dark Rey is the first person other than Darth Maul to be shown using a double-sided lightsaber in a live-action Star Wars film.
Sequel Trilogy
Just like in The Last Jedi, Rey checks BB-8's antenna to see it is properly set - she found it bent after the scuffle with Teedo in The Force Awakens.
Rey slides down an embankment into the Lars Homestead on a metal panel as she did on Jakku after scavenging the crashed star destroyer in The Force Awakens.
One of Rey's first scenes in The Force Awakens features her dreaming about becoming a Resistance pilot by gazing up at the sky while wearing a Rebel pilot's helmet. Here, she finally gets to wear one for real - Luke's.
Finn meets several former Stormtroopers who defected from the First Order after refusing to gun down unarmed civilians, just like he did.
Kylo Ren tries to enter Rey's mind during the opening while she's running the training course - pressing memories of her past, but she counters it immediately with visions of his past. This is similar to their Mind Rape tug-of-war in The Force Awakens.
While being briefed about the Sith Fleet, Allegiant General Pryde points out what a bad idea it was to put so many resources into Starkiller Base instead of a proper fleet. That very point has been brought up repeatedly in the Expanded Universe about the Death Star (and many, many other superweapons).
3PO still has no faith in R2's back-up system like he did in The Force Awakens. R2 proved him wrong again. (The rest of the map in The Force Awakens, 3PO's memory here.)
Rey chops several trees with a lightsaber during a training run not unlike the ones she chopped during her duel with Ren on Starkiller base.
Sharp-eyed viewers will notice that when Rey heals Kylo after stabbing him, it not only heals his chest wound but also the facial scar she gave him all the way back in TFA.
In The Last Jedi, General Hux briefly considered shooting an unconscious Kylo Ren dead, but stopped when Ren woke up. Here, he goes through with treachery by shooting the Stormtroopers who were about to kill Finn, Poe, and Chewie.
The Millennium Falcon has a hard landing similar to the one on Starkiller Base.
Finn and his companions are once again brought before a firing squad organized by General Hux. This time, it's Hux himself who saves him at the last minute.
A star destroyer above Endor is split in half, apparently due to a ship ramming it at lightspeed, a move Beaumont Kin called the "Holdo Maneuver".
Finn refuses to retreat when the command ship resets itself knowing he was on a one-way trip. This time, no one blocks him (like Rose did in The Last Jedi), but he does make it out alive from destroying the ship thanks to Lando and the Falcon. Also like in The Last Jedi, said attack involves him targeting a massive First Order vehicle armed with a Death Star-caliber turbolaser.
One of Finn's first acts of rebellion in The Force Awakens was launching a smaller craft from inside a Star Destroyer, using its cannons to cause damage to the larger vessel, and then fleeing in the smaller craft. Here, it's inverted: he lands on the surface of a Star Destroyer in a smaller craft, then hijacks the Star Destroyer's own cannons to destroy it from the outside.
Luke's first appearance in The Last Jedi had him tossing his father's lightsaber over a cliff in disgust after Rey handed it to him. His first appearance in this movie has him catching it after an anguished Rey threw it aside.
Rey retreats into exile on Ahch-To at the first Jedi Temple and is ready to cut herself off after defeating Kylo Ren on the Death Star II remnants. She is talked out of it by Luke (in Force ghost form), who telekenetically lifts his old X-Wing fighter out of the water where he had left it when he was there much like Yoda did on Dagobah.
Luke's Force ghost is able to affect the environment around him (making his X-Wing surface), just as Yoda's ghost made lightning strike in the previous film.
Finn again rescues a prisoner from a Star Destroyer. The first time it was Poe, now Poe assists him in rescuing Chewie.
Threepio gets Rey, Poe, Finn and Chewie to look at him in disgust when he's talking about the festival. This indirectly relates to everyone in the remains of the Resistance looking at Leia. In both cases, the target also looks in the same direction
A First Order Star Destroyer is shown crashing down to Jakku, to give the Imperial Star Destroyer seen in the beginning of The Force Awakens(named Inflictor) some company.
The search for the Sith world of Exegol mirrors the search in The Force Awakens for Ahch-To, birthplace of the Jedi order.
Anthology Series
Kijimi's destruction is very reminiscent of the destruction of Jedha and Scarif from Rogue One. Instead of an instantaneous explosion like Alderaan, the surface level of the planet is first destroyed as the laser bores into the planet, causing huge shock waves and planetary devastation, leading up to the planet exploding.
The planet where Kylo Ren finds the first Sith Wayfinder is Mustafar, the planet where Vader's castle was located. Very fitting as this Sith Wayfinder is actually Vader's Wayfinder (the other one in the movie is Sidious').
Lando is wearing a nearly identical outfit (featuring a yellow shirt with blue cape) to what he was wearing for most of Solo.
The Space Clouds that Kylo Ren, Rey, and the Resistance fly through to reach Exegol appear to consist of gaseous nebulae with landmasses floating in them, very visually reminiscent of the Akkadese Maelstrom in Solo.
Expanded Universe/Legends
The plot of Palpatine returning by taking over a clone body, and attempting to subjugate the galaxy under a new Sith Empire is very similar to Dark Empire. Along with that, Exegol bares some similarities to Byss, and the Xyston-class Star Destroyer is similar to the Eclipse-class Super Star Destroyer both featured in the comic. One wonders just how much of this is deliberate.
In Rey's vision, her Sith counterpart wields a double-bladed lightsaber with a folding handle, akin to the weapons of Pong Krell and the Jedi Temple Guard.
When Rey hears the voices of the dead Jedi speaking to her, the camera pans upwards to a field of stars, which calls to mind a similar scene from the final season of Rebels where Ezra hears voices from the past, present, and future in the World Between Worlds.
The design of Palpatine's temple on Exegol (a black stone ziggurat-like structure illuminated by lightning strikes) is strongly visually reminescent of the Sith Temple on Malachor in the Season 2 finale of Star Wars Rebels.
One of the background Resistance members, Junn Gobint, is a Mythrol, a species of amphibious humanoids with fish-like traits that made its debut in the very first episode of The Mandalorian.
Palatine's plan to harness the combined power of the Sith and, subsequently, Rey's harnessing of the combined power of the Jedi is very similar to Jerec's plan to do so using the Valley Of The Jedi in Jedi Knight: Dark Forces II.
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