I think your weapon of choice is going to be determined by your location and food acquirement needs. If you are in an urban environment, a shotgun (e.g Mossburg) with shot and slug rounds will be good for close in defense, in addition to a sturdy semi-automatic carbine with easily acquired ammo (e.g SKS) for longer range/general defense.
If you are outside the confines of a city (or can get outside the city) a scoped .303 is good for bringing down large game (e.g deer). A varmint rifle say .22 caliber can also be useful for shooting rabbits etc and is easier to cart around. ANY weapon slung is going to be an incentive to any nasty people out there that you mean business - especially when you point the business end in their face!
