That's a good list but it also depends on where your interests lie. It might not hurt to take an afternoon to tour Ft Sumter if you're a history buff. As a bonus you get a boat ride out in the harbor.
If the boat tour sounds good and history isn't as important, you might take a dolphin tour of some kind. October is one of the best months to watch dolphins. Captain Sam's Inlet down by Kiawah is a good place for it. If you do go that way, stop by the Angel Oak to see an incredible live oak tree:
Angel Oak Tree - Homepage of the GOD of all OAK TREES
Magnolia Plantation is a good spot if you're a birder.