Early in the movie, Bender (verbally) attacks Claire for wearing diamond earrings that her rich dad probably bought her: He hates such an ostentatious display of wealth and privilege. But by the end, Claire actually gives him one of her earrings—which, if it really has a diamond in it, is a super-expensive gift.

Bender puts it in his own ear, which symbolizes the lessons they've learned: They're not really all that different from each other. By donning the markings of a rich person, Bender is acknowledging their shared humanity… or something. (Plus, if things don't work out with Claire, Bender could pawn that earring for some serious cash.)

In a symmetrical, parallel instance of gift-giving (or gift-taking), Allison takes a patch from Andrew's letter jacket as a token of remembrance. Of course, they're probably going to see each other again when the school week begins, so it's not a "token of remembrance" in that she's never going to see him again. Like with Bender and Claire, it's a way of solidifying the moment of recognition they've all shared with each other, the sense that their experiences overlap.