A pretty standard rule of thumb is triple your ingredient cost:
It takes a little getting used to, but figure out how much one plate of food will cost wholesale. Include everything on the plate in basic ingredients. So say your pulled pork sandwich, slaw and potato salad cost you $4.00 to buy the ingredients. Here's your calculation
Ingredients - $4.00
Overhead - $4.00 (fuel, plates, all the support expendables)
Profit - $4.00 (No profit is NOT a nasty word)
Plate Price - $12.00
Your ONLY wiggle room here is how much you pay yourself. Don't sell yourself short! People always want freebies, I don't know about you, but I don't have the budget to feed the whole neighborhood for free!