When it comes to long-term food production, permaculture is often overlooked. You want to create the most nutrient dense foods with the least amount of inputs as they will be scarce. Example: Hazelnuts. grow on all kinds of soil. Doesn’t require fertilization/tillage. Nutrient dense and can make cooking oil out of it. Maple syrup. Yes a pain to collect but zero gardening. But If I had to plow land and could only grow one thing it would be soybeans. The only complete plant protein. After that potatoes
FYI - Quinoa grain is also a complete protein. I have tried it, and it’s pretty good.
There has been an ongoing controversy over the whether soybeans are actually healthy or not - which I have not followed, since I prefer real meat, and don’t buy soy burgers etc.