There's a LOT of marshy creek areas all around HHI - good for sea trout, flounder, reds. Sea bass hang around structure. You can use cut bait, of course live shrimp is great if you can get some. If the winds are cooperating, you can go out into Port Royal Sound and try the reef structure off Parris Island. If you haven't boated in this area before, make sure you have a chart and GPS to avoid grounding. The tide range is 7 to 8 feet twice a day ... make sure you dont get into skinny water too far on an outgoing tide or you may be staying there for a few hours. Getting back on the trailer or docking when the current is really running can be "sporty," so plan accordingly.
A great source for local up-to-date info and sugggestions is "Low Country Outfitters" just before you cross the bridge onto HHI. They are in the Moss Creek Shopping Center. The owners name is Travers. He's very knowledgeable about whats biting where and happy to help. The kids will love hanging around there and petting his black lab who is always in the store. It's also a great place for live baits.
Also, if you guys want a nice lunch/day trip, head across the Port Royal Sound (wind/conditions permitting) and head up to Beaufort. The Admiral will like that trip also. You can dock free at the City Marina and enjoy walking around Beaufort. There's lots of restaurants of all kinds.
Also, you might want to try posting at:
http://www.charlestonfishing.com/
There's a Beaufort/Hilton Head thread there.
Have fun and leave some fish for us - we'll be going right after Christmas.