This is an old one and kinda got off the subject. Let's see the question seemed to be in a survival situtation. Well I only use 16 ga shotguns anymore and have more rifle's,,,,, well forget that. But I've thought about this for year's.
22 mag, hand's down. If all I owned was a shotgun, I'm not gonna go looking for a grizzly nor likely even be where one is. If it's survival, I'm shooting the duck's on the water and I'm not wasting any ammo on a dove, not much eatin' there! But with solid bullet's I can kill deer or elk, either one, plus any bird that would make a meal. Furthermore I can carry a whole bunch of ammo in my pocket and it's a whole lot cheaper than anything other than 22 LR's. It's also a lot quieter so it won't attract a lot of attention in the process of getting dinner!
Like I said before, if I could only own one gun and wanted to legally hunt a variety game it would be the 12 ga., but as Don said if it was just about survival the 22 mag would be tops on my list too. That is one under estimated calibre. I know native hunters (they are allowed) using it on moose up here and are very successful. It takes more than one shot in the head but the moose doesn't even know he is shot. Evenetually it just drops down and dies. Not my cup of tea but considering my moose went 125 yds with a lung shot by a 300 RUM maybe he is on to something.
Benji...........Granted the 12 gauge pump is a great home gun for self-defense provided you can get to it quick enough OK.
However, for a caliber that would be at your side in the wild and wooley country of Alaska or Canada wilderness, I'll stop you short for just a second and mention the .338/06 for just one rifle that can do it all but pluck ducks out of the sky.
I mean this caliber is on a 30-06 case and brass is plentyful and it will stop a big grizzly in its tracks too! Chub Eastman of Nosler can tell you so for a fact.
You can load er down for taking deer or push a 275 grain Swift A Frame bullet in the magazine for the monster bears.......It's my pick for just having one gun dose it all, including predators too, with a Barnes 160 grain bullet.
When hunting whitetails there are many different languages being spoken afield that I key on when outdoors. All these little creatures living around whitetails have something to tell us if we are willing to listen.
My favorite tattletales of the outdoors are a handful of little birds that live in my state of Ohio. Maybe yours too. A tip for the upcoming season.
There are Blue Jays, Cardinals, Chickadees, Killdeer, and Sparrows that all have language...