My personal philosophy is that one should have a firearm for each birthday.

I like to have a minimum of four magazines for each detachable magazine fed gun, or four speedloaders for revolvers.
But as Glockman pointed out, if you can't get it done with a Glock 20 and a .30-'06, it's time to call in an air strike.
heh...heh..... If I had a birthday for each gun that I own, I'd have to be almost 400 years old....
"Minimum" serious weapons?
From smallest to largest :
1. S&W M442, .38 Spl Airweight revolver with at least one speed strip. (Always handy, can be toted concealed while wearing practically nothing, packs enough punch to get your target's attention.)
2. Glock 17, with at least four 17 round magazines. (Lightweight and relatively compact for its size and capacity, accurate, durable, reliable, easy to use and maintain. Ammo can be found almost anywhere.)
3. Ruger 10/22, with at least one extra mag. (Small game hunting, other uses. An accurate, small caliber rifle with a low noise signature has advantages for certain applications.)
4. AK or AR rifle, with at least 4 to 7 magazines at MINIMUM. (A whole bunch more at maximum. EVERYBODY should have one of these rifles, and preferably both. Some of the best short/medium range antipersonnel weapons ever invented.)
5. Winchester M70, Remington M700, Ruger M77, Savage M110, .308 or .30-06 scoped bolt action rifle. (Powerful, accurate, reliable. Either caliber will take down any North American game animal with a well placed shot, and ammo can be found almost anywhere. Can easily double as a "long range antipersonnel weapon".)
6. Winchester, Remington or Mossberg 12 gauge pump shotgun. (My pick is the Winchester Defender, but the others are just as good. Versatile and reliable. Uses range from hunting to home protection.)
Ammo? As much as you can afford, and as much as you can properly and safely store.
TR Graham
The Glocksmith