1) Do not use suitcases

They might me convenient for flights, but they are terrible on boats. The hard sides make them terrible to store. Go for duffel bags, they can be stored easily even when full.
2) Don't overpack on fancy clothes

Sailors are very laid back, and it`s all about function over form. But be sure to pack more than two swimsuits, since you’ll be wearing them most of the time
3) 3 towels per person

1 for sunbathing and swimming, 1 for showers and 1 small hand towel.
4) Bring a fleece

They are awesome at keeping you warm in the evenings, and dry if there is a lot of humidity.
5) A light sailing jacket

6) Foldable umbrella

7) Flip flops and boat shoes for men

For women don’t bring more than one pair of high heels, you won’t be able to store them and you won’t wear all of them.
8) Hats

Any kind will do, the sun is deceptively strong during the day so keep your head covered.
9) Books and or kindle

Sometimes there's no wind, and the best way to pass the time is reading.
10) Waterproof pouches

If your phone or tablet isn’t waterproof get some waterproof pouches, even it nothing happens you’ll have peace of mind.