You can camp anywhere on the coast of Gotland as long as you don´t camp on someones yard or on someones farmland. So don´t camp to close to houses and make sure there is nothing that grows on the ground.
East coast (Stockholm, Mälaren and Gotland)
Torö
Muskö
Dalarö
Åkersberga
Mariefred
Gotland
West coast (Gothenburg and Bohuslän)
Gothenburg/Fiskebäck
Gothenburg/Hisingen
Tjörn