Sailing brings you out into the sun. Which is gorgeous but also really strong when reflected off the water's surface. So beware of an almost instantaneous tan. To be prepared pack long sleeve t-shirts that protect your arms and upper body. And of course, the basics like sunglasses, hats, and sunscreen.
Pack your toiletries, although you'll find towels on board.
A personal first aid kit is a great idea. If you suffer from any kind of allergies do bring along antihistamines, or any other medication to keep the symptoms under control. It's important to keep in mind that a properly equipped hospital may be out of reach on some of the travel days.
Swimming suits, masks, and flippers — you'll be needing all of the above. Collapsible fishing rods are also a brilliant idea. The ocean around us will have supple fish so we can enjoy a delicious freshly caught meal!