What gun was going to be most useful? Why? Chapter 6

From the text:

Ammo. He had more than he would ever need for the big rifle, the carbine, and the shotguns. But he had only a couple of boxes of .22's, and he guessed that the .22's might be the most useful weapons he owned, if economic chaos lasted for a long time, a meat shortage developed, and it became necessary to hunt small game.