I am not big on guns. I don't even bother keeping any guns right now.
I used to have a few, but not now.

I will comment on your thread anyhow.

If I was restricted to one firearm for meat getting it would likely be a .22 single shot. Possibly a repeater, but certainly a bolt action, certainly with iron sights but possibly a scope in addition to the iron.
You chose semi auto. That is OK. They work too. The AR-7 is a nice light and easy to store package. Ideal for bush pilots.
A 12 guage shotgun would be the second choice, and something in the 30 caliber range if there was the likely chance of big game that needed to be shot.

Why .22 bolt action? It is reliable, the ammunition gun and ammo are both inexpensive and light to carry. It can be used on almost anything up to the size of a small deer with a pretty good certainty of success. They have killed larger animals but it starts getting pretty iffy. I would not want to try a bear or moose with it, yet people have killed bear and moose with them.

Shotgun? Because of the great variety of loads one gun is good for everything from rabbits up to bear and moose. It satisfies most SD needs if they ever come up too.
This would likely be a pump gun.
A shotgun has about the same range as a .22, or a pistol.
For me the .22 wins on ammo cost and weight over the 12 guage.
It is not easy to choose between them though because of the ability to use the shotgun with different loads for different game including birds.

About the .30 calibers. You know with 303, 30-06, 30-30, 308,etc a lot of different good calibers exist. They have good availability, they can be purchased for a reasonable price and will handle any animal in North America.
The only drawback is the weight of both the rifle and the ammo. Smaller game is just blown away to smithereens with them too. Again a bolt action for reliability.

I would be very unlikely to ever need a higher caliber like a .375 Winchester or Wetherby magnum and using one on anything I might shoot would just be wasting powder.
I tend to think of .223, 5.65 and all of the hyper velocity .22 type rifles as varmint guns. All very flat shooting, but not really great knock down power.
Good for shooting coyotes at long ranges, but not really good meat getters.
Also since I usually hunted forest areas most of my shooting was under 75 yards and only occasionally as far as 1,000 or 2,000 yards.
So no real need for long range stuff

About using crappy ammo.
Well for sure not. It might be OK for plinking or range practice, but not for where you want each bullet to put food on your table.

One thing about the .22 is that it is a trapper's friend.
A line of traps, deadfalls and snares will supply a lot of meat. Aircraft cable will get you more moose, deer and bear steaks than a rifle ever will.
But you might need to kill them even though they are in the trap.
A .22 lets you stay just far enough away to be a bit safe and a well placed shot will finish them off, even of it is just a .22.

Now for backups.
I would likely just get the parts most likely to break or get lost and store them. Things like springs and firing pins or clip parts.
If you want a scope you can get decent demountable scopes that let you still use the iron. If you put a redspot or quick point scope on you will likely just use that for everything anyhow.
You don't need high power scopes on a .22.
They don't shoot that far anyhow.
I doubt if you will ever shoot the barrel of a .22 out, no matter how many bricks of ammo you feed through it.