1. Middle Street. Sullivan's Island's adorable "downtown" strip has plenty of dining choices after a long day at the beach, from Poe's burgers to Home Team's barbecue to Dunleavy's pub fare (and free popcorn).
2. Free parking. You may have to search around a bit for a good spot, but parking on the island is free. Just make sure your car is completely off the pavement, and there are no "no parking" signs nearby (duh).
3. Fort Moultrie. This historic fort on the end of the island is surprisingly expansive and a little bit creepy. Moultrie offers unbeatable views of the ocean from the top. It's easy to sneak in, but it only costs $3 for adults to tour the place, and it's free for kids.
4. View of downtown. Walk to the Cooper River-end of Sullivan's Island, and you'll be rewarded with a unique view of downtown Charleston, not to mention the Ravenel Bridge, Fort Sumter, and Morris Island.
5. Picturesque paths. Some of the beach access paths are a bit long, but they're easy to maneuver thanks to a succession of well-maintained boardwalks. You'll typically pass through a section of woods before getting to the marsh grass and flower-covered dunes, then the beach. Lovely.