One gun?
12 ga 870 Remington express with a rattle can paint job.

If you have to consolidate everything that can be done with a shotgun into one,
Then you have to consider paddling a boat, swinging like a baseball bat, prying a car door open, packing inside an 18” boot, ammunition availability, repairability, and spare parts. Alongside of being capable of killing every animal on the planet, except for some mega fauna.

None better than an 870.

Out there doing it best I can.