You can fully cook potatoes (any variety) in the microwave and either eat them whole with toppings or mash them, I've never noticed a difference between this and boiling. Of course there's also dehydrated potato as well, you can heat water in the microwave and then use the hot water to reconstitute.

Canned beans are easy to reheat though canned beans are often bland, so you'd need some spices.

Oatmeal or other porridge grains. Just be careful about it boiling over as it will make a sticky mess.

Maybe invest in a rice cooker, the cheapest are probably less than 20 USD, and you could get a used one at a thrift store for $5 or less.

On the road I like nuts, dried fruit, and fermented things for snacking.