The shipwreck has a lot of potential. Make the island large. Wild natives, smugglers, pirates, a small coast town (soon to be under attack). It throws the party together with a nice starting story line. It could also be setup such that the entire party is needed to capture a boat/ship and only (depending on the number of PCs) the player PCs are willing to sail on the ship.
I've done something similar to this. It was great fun. I also used the non-weapon proficiencies. Only one character had sailing/boating so the PCs made him captain. This was great fun, since that person got into the roll of trying to command characters that did not know anything about a boat.
Note, a lot of this also depends on the people you are going to have. Are they roll-playing, or hack and slash? Either way the island could be turned into either type of game with a limited amount of work.