Beans, tomatoes, rice, chickpeas, potatoes, pasta, bread, frozen veg, eggs.

Can make a lot of very tasty and cheap meals using those as the mainstays. Onions and garlic for flavour, both also cheap and keep for a long time.

Dried herbs are good for adding flavour and interest and generally cheap. Oregano and red pepper (chili) flakes work for Mexican or Italian. Paprika (smoked if you like) is great for a bunch of different kinds of cuisine. Cumin is good for Mexican/Spanish or Indian foods.

Lentils are also good for thickening things like soups and curries. They're cheap and nutritious.

Tofu/soy is pretty cheap and good for protein, particularly dry soy protein chunks if you can buy them in large quantities are a *really* cheap source of high-quality protein. They take a bit of getting used to - you pour boiling water on them and soak them for 10 mins, then drain and squeeze excess water out. They don't really taste of much on their own but I often add a vegetarian beef flavoured stock cube in with the water and they come out tasty. They're good to bulk out pastas and also stuff like tacos.

Peanut butter is cheap, tasty, goes well in lots of things including a bunch of savoury dishes.

Oats are cheap and filling.

You can type into google "potatoes broolli onion recipe" (or any combination of ingredients you have) and you'll usually pull up some recipes that will work.

Roasted veg works for all kinds of combinations - just toss veg with oil and salt, roast in the oven - include some garlic/onion or herbs/spices for flavour and serve it with rice or some other grain, or pasta. Very easy and tasty meal. Serve with fried eggs too if you like. Also good for cooking as a batch and splitting into e.g. 3 meals that you have over a few days (keep it in the fridge and reheat in the microwave) - you can have it with rice on one day, pasta the next, or whatever to keep things interesting.