The proverbial "you're told you're going to be stuck on a large island, specifics unknown (but not Kodiak etc) for a year and allowed one gun". = 357-4 like the 686+. Everything from monkeys to Kraits to Komodos to a well placed close up shot on a water buffalo or even less likely point-blank tiger in a pinch. Same island scenario but you know it's going to be north of the 44th parallel or so - .44 Mag 629/Mountain Gun, maybe a 454 if specifically Alaska.
Dry land - similar set up but but maybe the 686 for desert Southwest, lower mountains and Great Basin, .44-4/629 for the Sierras/Cascades, southern Rockies, and a 454 for the northern ranges. Restricted to "civilization" and non-Rockies rural - .357 again.
Totally unknown circumstances --or you know it'll run the gammut with very likely rugged western rural to inner urban? - .44 Mag 629.Mountain Gun. Load it down or .44 Specials for urban "social work."