Until more recent times, a handful of hard boiled eggs was cheap, highly nutritious, and damned good with a sprinkle of salt/pepper/tajin/paprika/furikake or a dollop of mayo/sour creme/sriracha/nacho cheez/butter/etc. Potatoes are still pretty good in the same ways; just bake and let cool and you can add any of those same toppings and chow down at any time. Or get the smaller ones and airfry with a spritz of oil and salt. As long as you eat the skins, it's good nutritionally too.