A carpenter must own certain types of tools before he/she feels capable of tackling any type of project. Similarly, a serious shooter must have the right tools for the any given situation.
Does /k/ feel like there are certain types of firearms they must possess before they feel like they have a capable arsenal?
I do. I would say at a minimum, I must own:

A pistol
A .22lr rifle
A "deer caliber" rifle
A shotgun
A semi automatic rifle

Owning one of each of these types should cover most firearm situations.

WHAT IS YOUR MINIMUM?