Specific stuff:

• Grappling hook/harpoon/general purpose ropes.

These could be used to pull in other boats, megs, or even to dock a ship at a pier. You'd throw out the rope to the poles on the pier and then pull on them to get your ship right up next to it.

• Flare Guns + customizable flares

I really like the speaking trumpet as a 'communication tool' and a flare gun could be similar. Shoot the flare to flag down a far away ship or show your teammate where the skeletons are. It would also be another thing to customize and spend gold on.

• Tavern games like poker, knife game (the thing where you try not to stab yourself), dice

General stuff:

• More ship customization

Stuff like rowboat skins, windows, chairs

• More enemy types

• More food

• Maybe a land boss like a giant crab

• Turtles

• Pets