Dense energy source that doesn't usually have a strong flavor on its own, keeps well, and grows in a wide variety of climates? There are plenty of starchy plant

Dense energy source that doesn't usually have a strong flavor on its own, keeps well, and grows in a wide variety of climates? There are plenty of starchy plants - plantains, other tubers, taro - but potatoes will grow in non-tropical climates, which is a big benefit (and was an even bigger one before fast refrigerated transport). They're also easier to harvest by hand in usable quantities than, say, grains.