Hey SoccerKid -- here are my recommendations:
1) Good sunglasses! (Two pair if you've got 'em)
2) Suntan lotion
3) Bathing suits (4)
4) Shorts (2)
5) T-Shirts (4)
6) Lightweight linen pants (1) -- if you go for a nice dinner
7) colored shirt (1) -- if you go for a nice dinner
8) cash -- plan on $40/night at a mooring ball plus another $200/week
9) visa card -- not many places take Amex
10) crazy glue -- sounds weird, but it's far better than a band-aid for bigger lacerations. Always good to have around.
Now, it depends on what your charter company provides for the boat. You'll need to remember toilet paper, paper-towels, charcoal for the BBQ, matches, etc. You may want to order from Bobby's (Bobby's Market Place, British Virgin Islands - Supermarket, Villa and Yacht Provisioning Specialists
) terrible site, but GREAT service!
Let me know if you need more info.