The college I'm currently attending has a large majority of students who are activists for a plethora of different causes.
I took one look at that place during my college search yea so many years ago, smelled the weed, saw the giant butcher paper banners for every cause under the sun ringing the walls of the student center, and ran.
How many more years do you have left to serve, if I can ask?
Oh, and I love Eve's idea of hitting them up for YOUR cause, as well as Hester Moffet's idea that you should just guilt-trip them by saying your precious money is going to a poor starving Ethiopian, and don't they want HIM to eat?
Honestly, if it were me, I'd just tell people "No," and if they really started to get annoying, I'd buy more Easy Mac, Ramen, and boxed foods to make myself in my own dorm, and/or I'd go to eat at the cafeteria outside of peak hours. But, I'm boring that way
Now, if I wanted to get my troll on, I'd do one or both of two things:
1) I'd argue with these people about the political and social implications of these hand-outs---how hand-outs make people dependent on the Man, how they result in a decrease in self-efficacy and self-esteem, and how they convey our lack of faith in the other person's ability to be or become an autonomous adult. At least seeing people stammer, stutter, and have to re-collect their bearings would be hilarious.
2) I'd turn their own rhetoric against them, and play a "more liberal-and-principled-than-thou" game. Sniffing your money is going to Ethiopia or to inner-city rape victims is one way to play this game. Suggesting that people are practicing paternalism or colonialism, or are furthering the cause of globalization, patriarchy, or some variety of oppression by giving others hand-outs, is another. People often freak out when they think they're dealing with someone even more ideologically hardcore than they are.