Just had another thought on the subject. I wouldn't want to leave without a couple .22's. They would be on the top of my list. If you shoot CB cap longs...they are pretty quiet out of a rifle. But taking small game can be done with .22 Super Colibri's made by Aguila, 20grain bullet going about 500f.p.s.
I shoot those quite a bit, about as silent as you can get. They say for pistol only but I have never had a problem shooting them out of my rifles. They use only the primer to shoot. Try them sometime.
I have been thinking about getting one of the better ones, just to plink around with and hunt small game. I think Crosman makes a couple break action spring loaded rifles for under $150. They shoot much faster than my old 760 pumpmaster, and if they are of the same quality as that old 760, (it worked well for at least 15 years), I would definitely think that they could be useful in a SHTF scenario. Also, the ammo for them seems to be MUCH easire to find in quantity than even 22lr. And lets all face it, if the ammo situation is scarce now, It could become a commodity in a bad scenario. Also, I read a gun writer call 22LR ammo "ballistic wampum", so if you can find a way to conserve as much of what you have on hand for that purpose, an air rifle could be a nice supplement!!