When I used to work in downtown Toronto (pre-porn) my budget for food was like $3-4 a day and money all around was very tight.
I would get buns, sandwich meat, sometimes cheese, fruit and yogurt for all under $3. This would totally fill me up and was actually quite tasty!
When I got home I would 99% of the time have rice and some chicken breasts (if I could afford it).
DH