My favorite "poor" meal stemmed from a time I was very broke and quite literally had in my cupboard: a bag of rice, a can of pinto beans, a can of corn, and some diced tomatoes (I think I also had a few potatoes and a carton of oatmeal, but I didn't add them). So I mixed them together with chili powder, garlic, onions, salt and pepper. I figured it probably would taste ok, and pretty much just be something to eat. Yum! It made many meals, and I still make it now. Except now I can afford sour cream and/or cheese to put on top.
Other uber cheap meals of mine would have to be egg salad sandwiches and split pea soup.
I remember my grandma (who raised 5 kids in the 50s) saying she used to add extra rice or noodles to casseroles and felt bad about it years later, hoping her kids got enough nutrients. All grew into happy, healthy adults, so she must have done something right. My dad said she could make a can of tuna stretch to make 6 sandwiches (well, that was after lots of pickles and a couple hardboiled eggs

).
If you eat meat, you can take just one chicken thigh and boil it down and make a pot of soup, you can add pretty much any veggie (and lots of them) to chicken soup.
Oh, and hamburger soup. If you eat hamburger. Take a lb of hamburer (or turkey), brown and drain. Put it in a pot with a bunch of water, a chopped onion, about 1/2 a head of cabbage, and salt and pepper. Oh, and tomatoes, I don't know how much. Yum!