Since those days, even though I have family and friends to have holiday meals with, I've made it a point every year to have a small meal at the diner even if it's just coffee and a desert. And since I'm doing much better these days than a poor broke college student, I do it because I want to leave a large tip for the staff. No big Oprah style "you get at tip and you get a tip" performance or videos for youtube, just a simple card and big tip expressing my gratitude for them being there those years ago for past me, and for being around today for all the people who don't have anywhere to go still.
Whether they consider themselves exploited or not. Whether they're there because they need the work and the money, or (like I often did when I worked retail) they volunteered for the holiday shift because they had no where to be that day either. In either case, I was and remain grateful and the holidays are the one time a year I truly enjoy giving a tip.