I'm sorry that I don't have the Easter Saturday list of activities from last year handy, but on Easter Sunday last year they had the following activities: Pinckney Island Wildlife Adventure (small charge); Nature Kayaking Trip ($30 for adults; 17.50 for accompanied kids); Easter Egg Hunt (by age groups); Fun and Games at the Beach House; Egg--straoridnary Easter Activities (1 hr of egg-dying, face painting, arts and crafts, etc); and an Easter-themed Campfire in the evening. We went to the campfire but were in Savannah for the rest of Easter Sunday.
As for seafood, you will get a lot of different opinions. A local spot (also featured on the Food Network) is the Sea Shack. A bit hard to fine, but the food is good and inexpensive, but it is truly an informal place (picnic tables outside are the popular option). We also had a good seafood meal at the Crazy Crab (we went in Harbourtown, but many say the location nearer the bridge onto the island is even better).