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.
If you can get by on $10 a day in Sweden, that's pretty good. Beer is a heck of a lot cheaper in the States though so I'm not crossing it of my list of essential touring foods,
