We spent two nights camping on Cayo Costa...fantastic, memorable, buggy.
We took the ferry over, and had nice chats with Capt. Bruce & first-mate Joe (who has a funny story about his grandfather). It takes about an hour, then another 10 minutes or so on the tram to the Gulf side.
The tram drops off you & your gear at the "amphitheater", which is walking distance to the camp sites, then follows a loop to all of the cabins. Part of our group was in a cabin and the rest of us camped.
The reservations system through Reserve America was irritating and confusing. Why aren't there better maps and explanations of what to expect on the State website? Anyhow, we got off to a bad start. But once you see the beach (about 1/4 mile hike from the campsites) your daily troubles melt away.
The beach is pristine, quiet, long. The water is pretty clear, although the drop-off is quick; watch your little ones. We saw dolphins within minutes of getting in the water. And the sunsets were really stunning.
I would agree with other TripAdvisor reviewers who claimed this to be the "buggiest place on Earth". Rough night, even after smothering ourselves with bug repellant. Armies of mosquitoes, no-see'ums, spiders, gnats...and that was in the first 15 minutes. Semper Paratus.
The campsites were fairly spacious, although you can hear other campers easily. Some campers had boom-boxes going, one group was mangling Nirvana on acoustic guitars and the worst was the couple who carried on cellphone conversations...on speakerphone! People: turn your cellphones off! You're on vacation! I am, too! But everyone observed the 11:00 pm quiet rule.
Each night, we were visited by armadillos. We also spotted a 5' snake next to the tent. Bring a flashlight.
We rented kayaks for an hour, but could have done more. The highlight was seeing a huge dolphin meander right past our kayaks in Manatee Cove, a 20-minute paddle south of the launch. We also saw a croc in the Cove and a brown recluse in our kayak.
The bikes are simple but can be a tough pedal in the sand. Most trails are ground shells & pine needles. I took one trail to the northern tip of the island...a sweet, secluded spot looking across the turbulent channel to Boca Grande. Then I biked to the site of the old Quarantine House, where a plaque explains the history, and you can see the pilings where the medical examiner lived 100 years ago. The trail south of the campsites is also interesting, leading you to a gator-filled lagoon.
The staff people at Cayo Costa were all very friendly and helpful, including the ranger who helped us relocate the brown recluse, Mary the Tram Driver and the sweet volunteers in the gift shop.
Other than frustration with Reserve America and battle fatigue from fighting insects, our Cayo Costa Caper was fantastic. I would return (better prepared).