OREO cookies with milk. I've eaten a family size bag in one sitting more than once.
In college, the OP's question was frequently thrown around in our house. The biggest debate came on the subject of Whoppers (BK, not the candy). Could you eat 1 Whopper every hour, on the hour, for 24 straight hours. So, in total you'd end up eating 24. The Whoppers had to have all the trimmings (except cheese was optional b/c of the cost). Also, since you had to eat them on the hour, you couldn't eat 3 or 4 at a time, then take a few hour break. Noone was ever ballsy enough to try it. The house was split 2-2 between those who said it could be done and those who said it was impossible.