being creative with basics [foodstuffs] - what are your favourites?

With rising food costs, I thought I would re-visit my eating habits. I eat meat, poultry or vege dishes but my favourites are basic. For example, versatile baked beans [supermarket unbranded}:

1. with cheese

2. with vinegar

3. with brown sauce [Lidl]

What are you best hacks for eating simply and cheaply? Do you mind eating the same thing for several days?