Reese's whole "I traveled across time for you, Sarah. I love you. I always have" and pretty much that whole ensuing scene.
It's even more heartfelt upon second viewing, knowing that Sarah and Reese's love making conceived John Connor. By "loving a lifetime's worth", they're giving humanity a fighting chance.
Not to mention the photo John gave Reese of Sarah when she was pregnant. Reese states that he always wondered who she's thinking about to make her so sad in it. It's revealed at the end of the film that she was thinking of telling John about his father, Kyle himself.
Reese's description of Sarah's son-to-be, "I'd die for John Connor." as he's in fact John's father.
Kyle Reese has a literal Pet the DogMeaningful Background Event moment while Sarah is getting them a hotel room. That same dog actually saves their lives later by barking at the approaching Terminator, giving Reese and Sarah enough warning to slip away. Man's best friend did his part to save all humanity.
While patching Kyle up, Sarah can't comprehend all the things she'll do to prepare John for what's coming. He is certain she can handle it, but she says she doesn't want this responsibility. To reassure her, Kyle relates a message from John.
Thank you, Sarah, for your courage through the dark years. I can't help you with what you must soon face, except to say that the future is not set. You must be stronger than you imagine you can be. You must survive or I will never exist.
It's a brief moment, but during Kyle's flashback to the bunker and just before a T-800 starts shooting up the place, some kids are playing with toy pistols and aim them at Kyle. Even with his weary state (and his upbringing in a nightmare world), he still has the humanity to playfully aim back at them. If he had survived the final battle, he would likely have been an excellent father to John.
