This is what I just sent out to my crew for a charter in late may. Hope this helps.

What to Bring? The usual response is, half the clothes and twice the money.

Don’t over pack!!! This is very important! This is the
biggest mistake people make. You will be in your bathing
suit and cover-ups almost the entire time, also mostly with bare feet while on the boat.


This is a recommended typical list:
Cruising Essentials:

PASSPORTS, everyone needs a minimum of 6 months on their passports before they expire!!!
Life Jackets for the Boys! You can rent these from Island Surf and Sail if you don’t want to purchase/carry them. I have details if your are interested.
Hat (preferably with tie so we do not have to retrieve it from the Caribbean Sea), Visor?
Sun Glasses, polarized are best. A floating eyewear retainer is a good idea.
Regular & reading glasses if required.
Sun Screen, selections are limited in the Islands.
Personal toiletries and medications.
Aqua-socks or similar "in the water shoe" NOT OPTIONAL this trip!
Mask and snorkel only if you have good ones that fit you and you don’t mind having to pack.
Otherwise masks, snorkels and fins in various sizes will be on the boat for your use.
The Boys should have mask, snorkel and fins. Probably will not have kid sizes on the boat but these can be rented.
Appropriate snorkeling gear, some people like rashguards to protect from sun, dry fit type shirts are also good, you can rinse and hang out to dry for another day.
Beach towel for each person.
Reading material: Books, or digital readers.
$500 cash should be fine along with Visa/Mastercard. Am. Express is not widely accepted.
Camera, maybe disposable waterproof ones.
Favorite music, (iPod/iPhone/MP3 Player).
Movies if you like, the boat will have a DVD player and monitor.
Personal flash light is a good idea for finding things and moving around the boat at night.

Apparel

T-shirts /tanks, dry fit types are best, (3) (you will probably buy more while there)
Casual shirts (i.e. Hawaiian/Golf) (3)
Women may want to have (1) sundress?
Shorts - 2-pair
Bathing suits (2), Cover-ups/wraps.
Underwear and sleeping gear (decide on the appropriate number then cut it in half).
Deck or tennis shoes (1 pair), no black sole shoes, these leave marks on the deck.
Sandals / flip flops - 1 pair
Socks - NONE, mostly bare feet while on boat
Long sleeve wind-breaker, sweatshirt (very light) or similar for the occasional rain squall.


NOTES:

Dress for the plane trip from the above selection.

In your carry-on bag, I suggest packing a change of clothes, a bathing suit and basic toiletries (in case your bags are delayed/misplaced.)

Storage in individual cabins is limited, pack accordingly. No hard luggage, it’s too difficult to stow. A duffel bag that can be folded is ideal.

Most try to pack in ONE carry-on, I can’t because of extra boat gear/toys that I carry along, but it’s a very good goal.