Luggage scale. You will be packing wet gear. You will need to shift some checked items to carry on to get home. It was amazing how everyone was overweight as we were packing to head home. Water has weight. Overweight baggage fee is $100 for the airlines.
A double wall water bottle with a caribener was my choice for water. Use the plastic cut for the beer and rum punch.
The rest of the comments all sound right. Less shirts. You will buy one while there which will be a good clean one to get home in.
They will store bags that are not going on the boat. So travel clothes and shoes and other stuff not needed on the boat are easy to store. You won't see it in a week. But not tripping over it on the boat. Headphones and dry shoes. The clothes I traveled to and will wear on the way home are stored.
I slept in one bathing suit while the other was drying. Had one set of "dry" clothes that I didn't use on the boat. 3 bathing suits would have been better. 2 shirts wasn't enough, 3 would have been fine.
I saved room for a bottle of rum to bring back as well. There is a liquor store across the street (700?) that is cheaper than the duty free at the airport.
Snorkle, bring it. Those that swam to shore thought that was fun way of doing it.
Your #5, delete. You are already planning on a light jacket. That will do the same thing.
#11, I brought one. Good choice for shore excursions. Although I still did most of my pictures on my cell phone.
#14, I brought some. Didn't use any. Left them all on the boat. If you get some, go up one size. You want a stout clip to help the sail of a towel if the wind picks up.
#19 can be left in the shore bag. All I had on the boat were wetsuit booties and flip flops. Unless you are one of those people who sleeps in socks they are not needed on the boat.
For reference, I have done an early October trip. Winter I would expect to change a little.
