I heard that in WWII, some naval dude's primary weapon was a flare gun with magnesium-based flares. 4,000* a pop, good for starting fire, signaling ships, or melting the innards of any unfortunate creature that crosses your path. I'd take one of whatever the hell that dude had, in a nice waterproof case, with plenty of rounds.
I figure that if I melt enough wildlife, I'll have food and irritate PETA, who will come get me (and then I can eradicate PETA and steal their ship). Or I could set the island on fire, which might get someone's attention.....thousands of miles away. And, in a pinch, I could melt anything that threatens my life.
Or, maybe a Single-Six with a chunk of ammo, or a .44 with lots of Special and Magnum rounds. But since this is the Rifle forum, maybe an SKS--reliable, strong enough.