When you arrive at the base, your first order of business should be to hunt down a spare cooler from the dock staff. They can be hard to score, but are critical for keeping beers in the cockpit handy.
If you're provisioning your own boat, divide and conquer. Two supermarkets will have everything you need: one's a 10-minute walk, the other (Bobby's) has an arrangement with the base: they'll van you to the store and wait for you.
The masks and snorkels at the base are well-used community snorkels… if you've got your own quality snorkel, bring it. The available fins are fine.
Waiting around the charter base for any reason is torture. The squeaky wheel gets the check out done. Find your boat briefer and make it happen ASAP. Get off the dock, and out of the marina.
Make it personal – bring your NOOD Overall Winner flag as well as your yacht club burgee to fly, or state flag, hometown colors, whatever you have that tells the world where you are from.