My choice would be a .357 magnum revolver loaded with full throttle 140gr JHPs (which you can load yourself). The choice is based on the foundation of my convictions that the .357 mag is the best overall revolver for almost everything.
My second choice would be a 125gr JHP .357 mag.
For stopping people, I don't think you can beat the latter. It's got plenty of energy, excellent penetration and even works on animals. My preference, though, is a 4-incher because of its excellent pointability.
I have a friend who shot and killed a cougar while checking his father's fence posts on a ranch. The animal jumped out of a tree and charged my friend. He had no choice but to shoot. And even though he managed to make the shot with a .357 6-inch, he couldn't get a good bead on the animal with the longish barrel and he had to fire twice to hit it once!
I've read accounts where .357s have killed black bears, feral dogs, cougars, wolves and people. You get plenty of punch from the 125gr JHP to do all of the above, plus the full throttle loads will punch through vehicles and flatten tires (anyone seen
Duel, with Dennis Weaver?).
I was out shooting one day with a friend, and he'd found an old tire to shoot at, and his gun was a Smith & Wesson 60 snubby .38. He was about 3-4 feet from it and aiming at it when I stopped him. He wanted to shoot that tire. So I moved him a ways off and had him shoot at it from a distance and at a safe angle. He bearly made marks on the tire and not one of his shots punctured it. I told him that more often than not, .38 ammo from a snubby couldn't even punch through a car door.
If out in the middle of nowhere, or on a roadtrip, my first choice of a gun will be the .357 mag. It works on both man and beast, plus it makes a respectable amount of noise if you get lost and need to create a noise signal. By switching ammo you can switch from larger game to smaller game, or go to bear size game.
The Ruger is a great choice and a 4-inch tapered barrel is ideal. The S&W 66/19 and the Ruger Security-Six are both very nice pistols suitable for hauling. The GP-100 and 686 are good runner ups. Twenty-twos, in my opinion, don't really do much outdoors except nab squirrels and rabbits. The Ruger Mark II/III Standard, however, is great for small game and protection against humans.
The Ruger Security-Sixes
The S&W 66 4-inch is very easy to carry.
Ruger Mark II's rapid firing and ammo capacity make it
a great outdoor/camping pistol.