well, you would want something in a common caliber... SO, lever action handgun caliber carbine in 38/357 does the trick and are pretty sweet IMO... a 9mm semi-auto carbine is also a very good option.. (insert Kel Tec sub2k here.) An AR is obviously a popular choice in said situation, in 5.56 of course..
Honestly however, when all is said, one of the most durable and useful guns you will get for the money is a simple SKS... reliable as hell, quite accurate, and chambered in the most plentiful cartridge ever produced...
For more suggestions, I recommend you narrow it down a bit more as we only know you arent interested in an AK, a 22, or an AK in 22....
Handgun cartridge or rifle cartridge?
Carbine length or full length?
Also, the mods dont seem to take to kindly to the "teotwawki" threads... how's about we call it a...."up and go world upside down just in case rifle..."
AKA, a fun, dependable, and cheap to feed, light weight plinker.