Absolutely legumes. Dried chickpeas, lentils and beans will have a best before date of about 2 years from their packing date, which I believe is just due to legislative requirements in some jurisdictions (for example, some places require all substances for human consumption have an expiry or best before date, which is why things that can't go bad like distilled water, vinegar, salt, sugar etc have a best before date). Dried legumes will last decades if properly treated and stored. I keep a massive backlog of them I just rotate through as a food buffer (I ate like a king all through covid food shortages, shat like a champion too).
Some legumes will require overnight soaking and/or hours of boiling, but lentils and peas can be prepared in an hour or so. Learn a few different Dahl recipes, and you'll always have something delicious and nutritious to whip up as a side or to have with rice or bread. Chickpeas are also super versatile, you can make falafel, humus or use them in curries and stews. They have a really earthy flavour, which is great. Just be sure to adequately cook chickpeas and beans though; some can be midly toxic and make you incredibly gassy if not cooked right.
There are some pretty good textured vegetable proteins out there now. I bought some dried stuff in a big resealable pouch that lasts for ages. You soak the little bits in water for a bit, then use them like you'd use mince. It's pretty close and a good source of protein. Also as others have said, plenty of canned meat products out there. Aldi's tuna with olive oil is my jam. Also whole fresh chickens are cheap AF. If you can plan ahead, you can cook a whole chook then break it up into portions and freeze them. I do a Sunday roast for my family and that usually gets us two roast dinners, then a couple more dinners worth of leftover white and brown meat that we use for sandwiches, pasta dishes or just having on the side with other leftovers. That leftover chicken in a couple of pasta dishes will push us out to 5-6 dinners from one bird.
