Here are the slots I set out to fill in my collection and what I've filled them with. I'm almost done.
1. Service/Combat Pistol: .45 1911
2. Compact Pistol: XD 9sc
3. Service/Hiking Revolver: 5" GP100 .357
4. Magnum/Hunting Revolver: 5.5" Bisley .45LC
5. Plinker: Walther P22
Rifles:
1. Personal Protection/TEOTWAWKI: Romanian AK
2. Small Game/Plinking: Marlin Bolt Action (scoped) .22 and Ruger 10/22 (red dot)
3. MBR: M1 Garand (On the way!)
4. Big Game hunting: Nothing dedicated yet, though the M1 or 1903 would suffice in a pinch.
I only have one slot left to fill, and I think I'll go with 2. A long range .30 caliber rifle, and a 45/70 in either a single shot or a Marlin lever action.
As for a minimum...for me I would say a .22 rifle, a middle of the road centerfire handgun (Something between a Ruger LCP and a S&W 500), and a centerfire rifle would be sufficient for anything one is likely to need a gun to do.