Well, help me out. What do you have now? I may be all-knowing, but I'm not clairvoyant...
But, I can guess. Surely you have tent, sleeping bags, pads, stove and cookware, that kind of stuff. What you need is to fine-tune the current gear list for a marine environment. So be sure to take the following:
A whisk broom of some sort, for clearing sand out of your tent before you go to bed;
Chairs, so you're not parking your butt on wet sand or getting splinters from sitting on a log (here I'm assuming you're beach camping, yet driving pretty close to your jump-off point). The Byer Deluxe Maine Lounger ($45; www.byerofmaine.com) is just the thing;
Small nylon bags: Fill them with sand, attach your tent's guy-out lines to them, and bury them in the sand. They'll serve as tent anchors if the wind kicks up. Also, take a sheet of plastic to lay down under the tent, as sand can otherwise grind away at the waterproof coating of the tent floor;
Extra towels, for beach use and clean-up;
A good board game, such as Scrabble, for an evening around the campfire while it's still daylight. And a kite. And of course a Frisbee!
Plenty of sunscreen, and an extra hat or two.
I wouldn't claim this list is exhaustive, but that should give you a good start. Have fun!