McD's $1 McDouble (double cheeseburger) + big mac sauce (free-$0.30 depending on where you are, but usually free). It's not healthy, but it's cheap and easy. Adding big mac sauce makes it a way better burger.
Chicken Franks (brands such as Gwaltney) can often be found for around $1 / pack of eight. Not as tasty as beef franks, but super cheap. I'll eat half a pack with ketchup and mustard packets for lunch, and the other half for dinner.
Bananas. Mashed with peanut butter for "Banana Supreme" as my mom called it when I was a kid. And by the way mixing and mashing are not the same. There's bananas mixed with peanut butter, which is just bananas and peanut butter. Then there's bananas mashed with peanut butter, which is Banana Supreme. Then there is always the Banana Supreme sandwich.
If you want a lot of cheap nachos: stop by 7/11, grab the big "make your own nachos" container, set bag of chips aside, fill up plastic container with the a few pounds of free chili, cheese, and other condiments you want, place a few chips from the included chips on top of your pounds of chili and cheese as camouflage, and buy a big back of tortilla chips to go with your chili and cheese. I know some will say this is wrong, but I was given the idea from a 7/11 employee back in college. For less than $5, I could get chili cheese nachos for 10.