This is the first in a series of relatively short posts of potentially crazy, potentially profitable ideas for musicians to use. If you use them, you don't have to give me any credit, but please do write in and tell me how it worked for you.
It's a well known fact that the way to a (wo)man's heart is through (her) his stomach. It's also a well known fact that selling cheap food near concert venues is almost always a home run. Why not utilize both of those facts and cook for your fans? If you want to go all-out, buy yourself a taco truck (or similar food-serving vehicle) and use it as your tour van. Alternately, you could get one of those dorm-room pizza ovens and plug it in by your merch booth. The key is to have something easy to make and easy to sell, and the means by which to do both. If you cook it, they will come.