Shade! Very important.
Warm blankets/sleeping bags and some form of heat in case it's cold at night. On our boat one of those little hanging brass oil lamps does just fine. Turn it off when you go to sleep.
Layers of clothing. It could get very hot, but it could also be cold, especially at night and returning to the Bay Area. Lightweight long sleeves/long pants in case you get burnt.
Do we have to even mention sunscreen? But a full-brimmed hat too. I use a cowboy hat I got at REI; Jonathan uses a lifeguard hat.
Screens, at least on your ports.
Plenty of water and ice to keep it cold. Sure, a cold beer or two is nice, but drink lots of water too.
On the topic of booze, some wine to share with new friends. We like Bota Boxes, available at Bev'Mo.
You might think me a sissy, but I'm bringing a shorty wetsuit in case the water's a bit too cold for my liking.
Stink Eye, Laser 28