There is a lot to do ON San Juan Island besides American Camp and English Camp. We had gone there with our C-Dory when cruising in the PNW, but it wasn't until we took jobs with a whale watch company (and lived on our CD-25 for the season) that we found other cool places on the island: the alpaca ranch, the lavender farm, Lime Kiln State Park, all the various eateries in Friday Harbor and Roche Harbor, the winery, the sculpture park (at Roche Harbor), the views across Haro Strait from the road on the west coast of the island, the ice cream shop in Friday Harbor, the fresh made donuts at the Lime Kiln Cafe in Roche, riding our bicycles to False Bay, riding our scooters all around the island (great roads), South Beach (more rocks than the sand beaches we are used to). I'm sure I am forgetting plenty of things to do there.
You can get to English Camp by boat if you have a dinghy. You'll need some kind of land transportation to get to American Camp.