Download music on your phone as you probably wont have wifi. Then take a line in cable to play music on the boat speakers and a charger, so,e boats only have car chargers, call and ask...
If you are planning on cooking on board, pack a small cooking knife and grater, a pepper grinder (if you like fresh pepper) and so e small bags of herbs and spices (so you dont have to buy a whole jar for one meal)
Clips to attach your hat to your shirt collar, so when it blows off ypu dont loose it. Band for your sunglasses, same principle
Collar casual shirts to keep the sun off your neck. Lots of swim suits, you probably wont wear anything else in the day time
A wind breaker rain jacket for when the squalls roll in and you have to keep sailing
A sailing knife, a length of line, a inflatable ring or two (tie them onto your line off the back of the boat when you are at anchor and they are fun to swim to amd hang out on)
A waterproof torch, you can lower it into the water at night and watch the big fish or hold it and shine at the water and attract the fish in
A waterproof bag thingy to put your phone in and hang round your neck when you go to shore
Quick dry camping towels (they never provide enough towels for bathroom and beach use)
Biodegradable soap so you can wash off the back of the boat
A star chart
A mini pack hammock to hang from the rigging
A kite
Cards and dice games
An id book of fish/birds you might see