I'm probably somewhere at the lower end of food budgets. My menu is simple but fuels me well:
Breakfast: Oats, apple juice, banana, coffee
Day: PB and jam sandwiches, banana, trail mix
Evening: Beans, rice, olive oil

Under $10/day and (fwiw) vegan.

I broke it down, and my single most expensive food stuff was my daily three bananas.
I stock up at big supermarkets. Not drinking beer or wine will save you a lot.