My $.02

22, either lr or mag.

Here's why.
Your scenario is one of being isolated and possibly
on the move for an indefinate amount of time. This
means needing a large amount of ammo and/or being
able to scrounge for ammo. While the 12ga. would be
GREAT to have, the amount of weight and space required
for 1 box of the 12 would give you literally HUNDREDS
of rds of 22.
A 22 can kill most things that you'll want to eat, and other
things that may need killin. As long as I'm at home, I'll
have a shotgun. If I have to beat feet, I'm packing
my 22 and about 500 rds of ammo. Here's hoping it
never comes to that.

God bless
PK