Think of it as “people kibble”. Without shame, I would eat Cheetos as my solitary food item for the rest of my life (CRUNCHY, not puffs)
Pizza
Potatoes. I can make it into whatever I want and it has never disappointed me to date.
Water
If I can’t vary the recipe (it needs to be the exact same every time), I’d probably live off something inoffensive and bland. Like polenta with fried eggs.
If there’s some room for variation however it got to be stew. It’s still a stew if I sub potatoes with taro. It’s still a stew if I sub the beef with chicken or fish. It’s still a stew if I change the seasoning. You get the idea, right?
Would probably go for something very practical. Water would be ideal, as I could get it pretty much anywhere for free or very cheap. Or maybe I’d go for chicken pasta salad, just to have a meal that contains a decent amount of variation.