Aluminum Christmas Trees: At the start of the story, Della has only $1.87 to her name — and 60 cents of it in pennies. When this story was written, there were two cent and three cent coins in circulation, making it perfectly possible for Della to have $1.27 with no pennies.
It Was His Sled: Della sells her hair and Jim sells his watch, making their gifts to each other useless. Everyone knows the twist by now.
Unintentional Period Piece: It's easy for a modern reader to tell when the story was written; Della and Jim's apartment is a "furnished flat" that costs $8.00 a week to rent (and is described as "not exactly beggar description" but could be better) and they seem to be just getting by on a $20 a week salary. Clearly, it's turn of the century America.
Values Resonance: Inflation aside, things haven't changed much for the working poor since O. Henry's time: it's still common for more than half a household's income to go to rent. And poor people still want to celebrate the holidays and give gifts to their loved ones.
