Their are 3 beaches on Cape Cod that allow 4x4 trucks and campers on the beach.
Sandy Neck located in Sandwich MA and extends East towards Barnstable. The fee for Sandy Neck is around $100.00 for residents. Non residents can get on for camping some seasons, but have reduced the amount of vehicles allowed for the last several years.
Race Point in Providencetown is the most accessible 4x4 beach on Cape Cod. It is part of the National Seashore and subject to their rules. Camping is permitted and its the best fishing around from shore. Race Point is lots of fun. People come from all over the world to see this part of Cape Cod.