Skeleton ships: On a sloop, you have the ability to weave about faster than the skeleton ships (yes, their AI makes you do it, so don't say you can't), and put cannons into their stern or bow while avoiding the worst of the cannon fire. Alternatively, you can charge an island in a straight line and pull away at the last second, which will cause the skeleton ship to get stuck and despawn.
Volcanoes: Don't go in the Devil's Roar. It's as simple as that. If you want to go into the Devil's Roar, you need a crewmate to help repair the ship, so if the one on deck dies, the ship will stay afloat.
The Kraken: Just ignore it and sail straight ahead with full wind. If the tentacle wraps around your ship, attack the end of the tentacle (the end will always be nearby, either hovering next to you screaming at the ship or actually on deck) The lower down you attack the tentacles, the less damage they take. Attacking the ends is far easier.
The Chest of Sorrows: If you don't think you can handle it, then don't take it. Stash it away where you can find it and come back later, with the intent of beelining straight to the outpost nearby. If you are dedicated, rowboating it back should allow you to not have to deal with the water. If you do take it with you, place it on land whenever you leave the ship. If you are attacked, don't be afraid to drop it in the water. Whatever else is on the ship is worth a lot more than that chest.
Hope this helped, but this game just went through a major update and needs some new balancing, so sorry about that. Keep in mind that it isn't meant to be an easy journey, and if you ask the right people, I have met galleons who love to help and guard solo ships.

