All of these are in Florida
Bahia Honda State Park, however getting a site there makes getting one at Yosemite easy by comparison.
Pirates Cove commercial CG on Key Largo has some sites right at the waters edge, but it's not exactly like camping on a beach tho you could be swimming within 10 steps or so from your TT.
Anacostia SP, Ft Clinch, St George SP, St Andrews SP and the other state park campgrounds in the keys are all close to the beach but not right on it. There are probably others that we haven't camped at. Grayton Beach for one. Jetty Park county park is close to a beach but maybe a couple of hundred feet away depending on which site you got.
