I'll second grislyatoms's advice to get to Ocracoke if you can. The NC Ferry System has schedules on the 'Net, and I think that the boat trip from Hatteras to the northern tip of Ocracoke Island is still free of charge (half an hour). Boats from Cedar Island and Swan Quarter (which go to the other ferry landing, in the village, I think) cost some bucks, IIRC -- it's also a much longer ride.
If you like to camp, the National Park(ing) Service campground a couple of miles north of the village is decent. Make reservations a couple of weeks beforehand if you can. Sometimes they used to have vacancies if you just showed up, but don't count on it.
Take insect repellent if you'll be around the dunes or at the campground (anywhere along the Outer Banks, really). There are biting flies sometimes, but they're tolerable. Sand burrs, too, so have some sneakers along for your feet (you can probably guess how I know this). Flip-flops or Teva-style sandals are good. {EDIT: flops and Tevas are good wherever sandburrs AREN'T, that is. Sneakers in the few places where they're heavy -- such as on the dunes}
Spend some time walking around in the village. Try to eat a lot. On the harbor and in town, and Hey Grisly! ...is it Howard's Pub that's just outside of the village, near the airport? A hundred kinds of beer and some burgers & seafood; that kind of place.
I regret not having taken a hang-gliding lesson in the Kill Devil Hills / Kitty Hawk area. You can also do some surfing along the coast; talk to the locals. At least take a shorty foam board if you don't want (or don't have time) to take a lesson on a real surfboard. Go swimming in the ocean; it's wonderful. Ask first about undertow and currents in the area, and swim near people who know the beach.
TAKE A KITE! Sam's Club had good ones, cheap, at least last summer. Triplanes and pirate ships as well as regular-shaped ones. These are the kites that need a lot of wind to work well, and the Outer Banks beaches are perfect for them.
Oh, yeah: windbreaker, a cotton sweater, T-shirts, shorts, some baggy Khakis to go over the shorts in the evening OR after the sunburn sets in, and a STRING to go under your chin from your cowboy hat / beach hat / floppy hat / Tilley Hat. I once did the 440 Hat Race along the (not steep, but definitely sloping) beach, in second place for most of it behind my straw cowboy hat. I put a string on it immediately afterward.
Take sunglasses to keep wind and sand out of your eyes.
Have fun!