I don't have much time to buy in bulk, prepare them for freezing/canning or chase prices. I follow mostly what is said before, never buy precooked stuff and so on. What made a huge difference on my budget is to learn new recipes. At first it was completely unintentional, I am trying to get on a better diet. There are many recipes that will fill you up with minimum number of ingredients. You don't need everything in a market to cook. Simple-cooking, as I call it, is cheaper, way faster and -I think- healthier. Search for recipes of the world cuisine that have 5 or less main ingredients. Or try to simplify your recipes.
Couple of examples might be,
Chılbır, boiled eggs (boiled without shell) put on yogurt with garlic
Pumpkin desert, cut pumpkins into pieces pour on some sugar and put it into the owen. If you have ginger, you can add some.
Mushroom casserole. Cut mushrooms into two or three, add some chopped pepper, butter, tomatoes if you have any, salt oil etc and straight to owen.
Flapjack with honey, just recently shared by way out west blow-in blog YouTube channel.
You can make hundred different of meals by salad, egg, rice or pasta being the main ingredient. Fried chicken with salad, menemen and so on.
You can find many simple recipes for carnivorous diet too. Grilled heart (cut in leaves) for example. Heart goes cheap here compared to other parts of the animal.
Freezer always helps if you have time. Fish is seasonal in Istanbul. You can buy wild fish when it is cheap - also meaning it is its season. Cut bonito into two longitudinally -like fillet- but with bones and skin. Put some tomato sauce, oregano and salt, straight to owen.
Sorry for any typos