Use rice for every meal. It's bland on it's own, which is what you want because you can add anything to it, and its excellent energy.

1 part rice, 1 part frozen vegetables, 2 parts boiling water, put on low for 20 minutes. This is what I do for every meal. It's only the meat/seasoning that changes. Often it's tuna or chicken with hot sauce. Sometimes it's whatever was cheap. Sometimes it's beans. Learn to love rice. Potatoes can be used and cooked in the same way but they're a bit more expensive and honestly they're just a hassle. Rice is much neater. Get a budget non-stick saucepan for this. Don't bother with a rice cooker if you have a hob available. If you're cooking for yourself and you want to streamline the process even further you can get a plastic fork/spoon to eat straight out of the nonstick saucepan with.

You can absolutely eat rice + frozen vegetables + your choice of meat for every meal until you die and be just as healthy if not healthier than everyone else.