I buy whole foods, meat, veg, fish, fruit, porridge oats and flavour ingredients (herbs, spices etc). Small amounts of hard cheese like parmesan and semi skimmed milk. Wholemeal versions of pasta, couscous, bread. Brown rice.
No processed food, no cake or biscuits, sauces, processed desserts, snacks etc. No alcohol. No fizzy drinks. Don't have them in the house. I don't spend a lot, £55 a week feeds us both.
I cook from scratch (which takes 30 mins each evening). If I want a cake or pudding, I make it, which means extra work, and so I bake once a month at most.
No limits on how much we eat. We are both slim. At 60 I'm a size 10 and 5'8". DS (14) is teen skinny.
It's not only the calorific value of what you eat. It's what additives your food contains. Stick to fresh, unprocessed meat or fish & a wide range of veg, you'll be healthy & food will taste great.