>>63842743 (OP)
If you're going out into the pure wilderness and there are no bears just take a 10/22. Kill and eat squirrels. You can buy and carry a metric fuck ton of ammo. Ruger 10/22 is the ultimate survivalist tool.
>>63842743 (OP)
12 gauge. It's ubiquitous, versatile, can be reloaded with hand tools, adaptable for black powder, and its manufacture is about as simple as you can get while still being a self-contained metallic cartridge. If society ever loses the ability to stamp out shallow brass cups, we're past SHTF, past "dark age", and gone straight into "near-extinction event".
>>63842989
I'd install stairs that are less retarded than a shit ass gay spiral staircase
and a cargo elevator would be nicer than hauling literal tons of stuff by hand in and out of there
>>63842743 (OP)
If you're gonna be out and about, your best bets for ammo that is versatile and you can get a lot of would be .22LR, 9mm, .223, and 20 gauge. Pick your favorite.