Here's my personal essentials list, not including an exhaustive clothing list, cosmetics, books, jewellery, etc.:

4 pairs of shoes:
- reef shoes
- running shoes
- sports sandals
- dressy sandals

Sun gear (I have a sun allergy):
- longsleeved shirt, treated with Rit Sunguard, for deck and beach use
- snorkelling t-shirt, ditto above
- two pareos
- 2 hats
- lots of SPF 45 or 50 sunscreen
- good sunglasses (for reading as well as distance)

Water and beach:
- bathing suit(s)
- reef shoes
- beach bag
(I don't bother with the air mattress, since have to sit or lie in the shade, so I don't get to float around on top of the water much!)

First aid:
- reactine (antihistamine)
- disinfectant wipes
- lip balm
- bonamine (seasickness)
- afterbite (for insect bites)
- bandaids