I think in-game rewards (or punishments) for OOG actions is one of the "cardinal mistakes" a GM can make, right up there with plot rail-roading and "precious NPC's". "GM's Girlfriend", arguably the worst mistake a GM can make, is simply an extreme case of this behavior. Minor cases are minor mistakes (not to be confused with "okay"), so I wouldn't make a big deal of it if 100 XP is all it is. If the richest player happens to be 2 levels higher than everyone all the time, then it's a problem.
Generally, it's best for all players and the DM to pay for their own "munchies". Any deals that are worked out shouldn't have anything to do with the game. I was "teased" a lot (I called it "bullied", but maybe I was being over-sensitive) as a kid because my parents didn't have much money, and I think when someone plays D&D they should not continue that attitude.