I already have the two rifles I would need for this hypothetical hunting experience:

Krieghoff "Teck" O/U double rifle in .458 Winchester Magnum, with interchangeable barrel sets in .375 H&H and 20gauge 3" Magnum.

Mauser 66 in 7X66 SE vom Hofe, with interchangeable barrels in 8X68 and 9.3X64.

They are not my most cherished guns, but they would do the job on anything I would care to hunt worldwide. If I had to go somewhere where ammunition resupply was a problem, then my old 7X57 on a G33/40 action or my pre-64 Model 70 in .300 H&H would serve nicely as a second rifle in place of the Mauser.