James Island has a pier inside the park on a tidal creek that you can kayak on. The tidal creek is big with access even at low tide. From there you can paddle only a short way out and be on the Stono River. Would be a long ways, but if you timed the tide right, you could go as far as the ocean and up behind Folly Beach.
The shuttle I believe is $10 each for round trip. You can take it either to downtown visitor center where another shuttle will take you to various parts of the pennisula, the convention center which is only a few blocks from the market, or Folly Beach.
They also have a climbing wall, disc golf course, dog run area with beach, and among other things.
It is only 20 miles from my house, but when we had kids, we would spend a few nights there, even if it meant I had to commute cross town.