Most of my shooting is geared toward survival situations, either as an individual or as part of a group. With that in mind, I've established a *suggested* list of firearms one should own. For this list, I've tried to consider all survival aspects - combat, personal protection, small game hunting, and large game hunting.
"Sniper Rifle" - My personal feeling on this category would be a rifle of at least .308 caliber - if your situation warrants it, even a .50BMG like the Barrett. I know - there are a number of perfectly adequate hunting rifles on the market in smaller calibers. If you feel comfortable using one, go for it. This rifle must be able to deliver accurate fire to ranges beyond your "battle rifles." To me, this means at *least* out to 400m. At *least* - especially considering many "modern" "battle rifle" or "assault rifle" rounds are only effective out to 300m or so. Some "battle rifle" choices are also used in the "sniper rifle" role, such as the M1A/M14. If you decide to standardize with one of these rifles, at least one should be equipped with a "quick-detatch" scope-mount. Obviously, long-range shooting requires more training than "mere" "combat shooting," so be sure to factor that into your training.
Shotgun - Here, I opt for a 12 gauge. According to the folks I've talked to, a pump-action seems to offer the most versatility. Also, try to get one with a 3-inch chamber. This will let you use just about any shotshell on the market.
.22 rifle - Excellent for small-game hunting and for teaching the novice shooter.
"Battle Rifle" - Here we have opened several cans of worms. By this, I mean the rifle you intend to use for "general duty" shooting, whether it be hunting or combat. My personal feelings on this category are that it should be semi-automatic and have a detatchable magazine. Others find a lever-action in a "pistol cartridge" adequate for them.
Pistol - The purpose of the pistol is to be carried at all times. It is there to deal with any "unpleasant surprises" - not to arm you for combat.
I suggest using one of the "popular" calibers for your weapons. By "popular," I include any cartridge that is in current use by a major military or is widely used by law enforcement officials or sportsmen. This includes:
This list is by no means complete, but should be taken merely as an example.
How much ammo should you have on hand? Tough question. "As much as you can afford to purchase" is my best answer. I won't ever stop buying ammo as long as it is available for sale. What I don't shoot, I store. Just remember, you may not be able to rely on running down to the store for more.