I believe in a worst case upheaval firearms and ammo will be among the most common items of barter. At the local pawn shops and garage sales you can find .22 rifles in a variety of makes and condition. You can often refurbish rifles that are in poorer condition. The .22 is very versatile. The ammo is cheap, it will kill a wide range of game and it can be used for self defense in skilled hands.
In larger caliber the Chinese SKS is a bargain.
Individuals have their own knowledge and preferences on this issue. And I'm preaching to the choir on FR. But the bottom line is a secure stockpile of firearms and ammo can be worth more than gold if things go south.
I have been an advocate for pistol caliber rifle and handgun pairing for years now. There are excellent and yet inexpensive carbines in 9mm and .40 cal (using Glock magazines), as well as lever .22 magnum, .38 spl, and .357 magnum weapons available. Nice to have same ammo for both pistol and rifle, with the rifle adding some to the feet per second of the rounds giving them more hitting power. A .357 lever rifle will bring down just about any North American mammal, except maybe griz or Kodiaks.