Lots of beans and rice. So many different meals with beans and rice.

A garden. Or knowing someone with a garden, at some point we all get an excess of something, I gave a big bag of jalapenos to our yard guys at the end of the summer, they were so abundant.

We do use the Too Good to Go app, but not many participating restaurants here, it's more for a treat.

Working at a restaurant that feeds you, I used to work at a place you could come for supper (teatime) before the evening shift. Not a chain place.

Set aside some part of the weekly budget for oil, spices, seasonings, chili paste, condiments. With these you can build variety of flavor into a basic cheap diet and they last awhile, you don't have to buy all of them each time, but always buy some.

ETA: planning the week of meals saves more money than trying to buy cheap foods, for me, but we still have kids at home so the calculation is a little different. I just don't like to - so I make a loose framework, know about 4 of the 7 meals, and keep dry/canned beans and pasta and rice on hand, and there is usually some veg in the garden, so I can leave some room for improvisation. Even that level of planning does save money.