Here's mine:
Ruger 10/22
Remington 870 12guage shotgun
Remington model 700 deer rifle. ( have one in .243 and 7mm Mag

I love my .40 XDm but wouldn't say it an absolute must have like my .22, 870 or 700's..

Remington 870
Marlin 336
Ruger Redhawk revolver

Doesn't matter about calibers/gauges.

Ruger 10/22.

I am lucky that I have all of these.

.22magnum .270 or 30/06 .223 would cover you pretty well

Remington model 870 Super Magnum Express 12 guage shotgun

Remington model 700 chambered in .30-06 (I'm OK with a Winchester model 70 chambered in .30-06 also)

Any .22 LR

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That is a short list, but that covers the ground pretty effectively. Of course, I do have other firearms that I treasure and value, but the question was what is "esential," or at least that is how I interpreted the question.

Just like on the politics board Im agreeing with Al as usual.