WWJWD? has a post up on the survival virtues of the rimfire rifle. Good reading, but I'd like to make a couple of additions:
1) On the value of ammo:
Jeff Cooper once referred to .22LR ammunition in a future crisis situation as "ballistic wampum". Even in the absence of a world where shirtless guys are running about the desert with colanders strapped to their faces, this description rings true. Ammunition prices are inexorably tied to metals prices, and with metals looking to stay expensive, ammo isn't going to get any cheaper. I make a habit of trying to buy a box of .22 every day. True, I shoot every day at work, but I rarely use the whole box. The remainder gets dumped into ammo cans where it will sit until needed for shooting or as trade fodder. Simply put, you can never have too many .22LR rounds on hand.
2) On useful rifles:
The Ruger 10/22 is, no doubt, an excellent rifle. It has ascended to that plateau of firearms ubiquity (shared only by the M1911, AR-15, and Remington 700) where you can build a complete example of the gun, from the ground up, without using a single part from the original manufacturer. However it is slightly hampered in the versatility department by its box magazine feed. Two equally excellent tube-magazine guns, the semiauto Remington 552 Speedmaster and the lever-action Browning BL-22, will feed shorts, longs, and long rifle cartridges, as well as functioning with colibris, CB's, and shotshells (albeit as a manually-operated straight-pull, in the case of the 552.)
3) The training option:
If you're a user of the 1911 and AR-15, Ciener makes conversion kits for both your pistol and rifle. Cheap training, small game hunting, and pest control with your primary sidearm and long gun.
A Gemtech Outback II is less than $600 out-the-door, including TN sales tax and $200 tax stamp.
H/T to SayUncle.