No one handgun can cover that wide of a range successfully so the best thing to do is chart the bell curve for each person's situation and chose one to cover the most ground in the middle of it.

First thought was a Glock 17 or like Bristoe, a .22, most likely a Ruger target model. Reason would be ammo availability in the Apocalypse since everybody and their brother's dog has one. But we're still 7 days from An Actual Apocalypse and 9mm and .22 is almost nowhere to be found and hasn't been for many moons, because everybody has one.

So I'd take my 6" GP100 half lug and all the .38 and .357 brass plus propulsion components already on the shelf, plus sufficient #2 alloy in the garage.

.38's for target practice and small game hunting.
.357's for marauders both two and four legged.
Concealed carry might be a problem. Oh well, Idaho is open carry.


Now change the question to a Three Gun Apocalypse, and the answer would be the same revolver, .223 rifle and 12 gauge shotgun.

Gunnery, gunnery, gunnery.
Hit the target, all else is twaddle!