Our first 3 trips we were blessed to go with friends who sailed and had been to the BVI more times than they could remember. Some of the great info (that has not yet been mentioned) as we were newbies.
They stressed packing light and suggested packing your clothes in plastic bags, helps save space and keeps them from getting damp.
If you run short on clothes, take them in the shower with you and let the water run over them as you take your quick shower, quick rinse and hang to dry. How dirty are they really anyway
Always Always Always have a bottle of water in your hand and drink more water than you normally would.
As for medical conditions, medicine etc ~ our friend who chartered the boat and was Capt had each of us list any meds, allergies to meds or conditions that may be important to know about in an emergency & place in a sealed envelope with our name on it. They were kept in easy to locate but safe place if needed and returned to us after the trip. I thought this was a great idea and respected our privacy, yet also would have helped us if needed.

Flash forward a bunch of years and now I am the trip planner. We hire a Captain and do our own cooking.
One thing we do that helps us out is bring some precooked, frozen meals with us. We eat 2 meals on the boat a day and one out. Having everything precooked and vacuum sealed makes for quick cooking and cleaning up. More time for fun. Someone mentioned everyone going to the store is chaotic...YUP! This year I am going a day early to do all the shopping etc to make that easier. When everyone else gets there the food and stuff will be loaded on the boat. Less stress!