Here's my picks for guns I think I should own, and I also think it'd be a good baseline for everyone to have for a well-rounded collection. I'm keeping this pretty generalized versus saying "XYZ particular gun in ABC caliber" since there's a wide variety of great choices.
.22LR pistol.
I have my Ruger Mark II 2245, but there's plenty of good ones out there to choose from.
Ruger 10/22 rifle.
I want one of these for a variety of reasons, but mainly so I can shoot that squirrel at 400 yards (GRIN)
A defensive semi-automatic of your choice in 9mm, .40, .45ACP.
I have my XDm in .45ACP. there's a lot of good guns to choose from.
A defensive revolver such as a .357 magnum.
A bolt action rifle.
A shotgun. Remington 870 comes to mind as a good old standard shotgun to have and own. I also like the Benali M4.
An AR-15
1,000 rounds minimum for each gun in reserve ammo, plus whatever ammo you shoot. I'm personally trying to get up to 10,000 in reserve in .45ACP and 25,000 in reserve for .22LR, but not sure if I'll make those goals because if I do, I'll still need more ammo to use so I don't go below those minimum numbers. I am getting closer though on each one.