I have found the Cook For Good website and basic cookbook to be a good resource, but of course if you're broke you don't have money to spend on a book. However, she has plenty of free recipes on her site an in her newsletter. My summary here includes some of her ideas, some of my mother's, and some of my own.
- Buy for maximum nutrition, not calories. Nutrient-dense is a better use of your money.
- Buy versatile and cheap "pantry" ingredients and make them work in multiple recipes.
- Beans are your friend; they are cheap and easily flavored in multiple ways.
- Borrow a principle from every traditional culture everywhere and stretch one food to make several meals. Bake a chicken, make stock from the bones, use the leftover chicken to make soup. Cook a big batch of beans and eat with rice the first night, then put the rest in a soup or bean salad or mash and refry them for burritos...etc.
- Buy fresh and in season, and use every bit of what you buy. Peelings and ends should go in stock. Fresh "conventional" fruits and vegetables are better for you than packaged "organic" ones. (Just wash them well to get rid of any pesticide residue and you're good). Put the organic fruit-on-the-bottom yogurt back and get plain yogurt and fresh fruit; you will eat less sugar that way too.
- STOCK. Make stock out of everything. Chicken bones, beef bones, odds and ends and wilted vegetables.Then use the stock to cook beans, rice, vegetables, etc. That way you don't lose any of the nutrition you paid for, AND stuff tastes better.
- Reuse other things too. Leftover grains, vegetables, and legumes aren't leftovers, they are ingredients. Put them in stock with some spices and you have a whole new meal.
- Make your own bread. Even cheap bread is more expensive than home-made, and yours will be more nutritious. Also, every kind of bread in the world can be made into toast, bread pudding, and/or dressing.
- You can make cheap and nutritious desserts and you should. It will add to your calories and nutrition and keep you from feeling deprived. Home-made rice pudding (made from leftover rice!) is your friend.
- Sodas on the other hand are too expensive for what they are. Drink tea instead.
- Learn to forage. It's blackberry season where I live. Half the stuff growing in my yard is edible in a salad. Even in an urban area like Atlanta, there is free food growing by the side of the road if you know where to look.
- Grow food if you can, even an herb in a pot in the window means flavor and nutrition you don't have to buy.
- Finally: The biggest detriment to someone struggling to make ends meet is our current cultural attitude that it is some kind of moral failure. That is bullshit, and it's not even part of actual traditional American culture, because our ancestors were smarter than that. Whoever set it up so that smart, motivated, capable people in the richest country in the world can still be poor is at fault, not you. Mentally tell them to kiss your ass and keep moving.