`I have no idea as to the kind of threat one would want to arm themselves against while sailing. It seems to me that any professional pirate would have the typical sailor outgunned. No one is going to "declare" themselves until they had the upper hand. Any other threat would seem to come from someone who had ingratiated themselves into the boaters confidence, and be aboard. But then again, weight isn't a problem and one could have several different weapons.

Hiking and backpacking is a bit different. Bears, maybe coyotes, and some of the cat family might be threats. The bears would require a large caliber rapid firing weapon, which would suffice against anything else. Including humans.

Snakes aren't really a threat. By the time you would have gotten ready to shoot them they'll be gone. Or it's easy to walk around them. At least that's true for the snakes I've run across on the West Coast. They would prefer to not mess with you.

People can be a problem, but it's best to stay away from them or find strength in numbers. A readily available small handgun would be best, but wouldn't be good against bears.