The cockpit lighting on Day One is very good. I don't think you need to bring any light for the cockpit.
I would bring snorkel and mask but leave the fins at home. Pick up the fins from CYOA.
I assume you will need to check a bag. And if you do I would bring a couple of sharp knives assuming you are doing any cooking on board. I will guarantee you the knives in the galley are pretty dull.
Other things you might consider:
- Ear plugs
- I bring a 50 ft 1/2 inch nylon line to use as a preventer. Doesn't take much space. Just in case I want to use one on a down wind leg
- Bring two or three of the large contractor garbage bags - the lines that are probably something like 50 gallon bags. We find these handy for bagging up two or three kitchen bags wroth of garbage and putting it in the forward hold. Just in case you can't find anywhere to dump garbage for a couple of days.
- I bring a zip lock bag with four or five Tide pods for when we stop and do some laundry at Leverick
- And another zip lock back with a couple of pieces of SoS steel wool pads for cleaning pots if I need them
- A bundle of paracord. Again - takes no room but 101 uses for some paracord.
- Raingear. At least the jacket part.

Life's short - sail more!