I use the white foam large flyboxes for stripers and dropped in on Monomoy one day. It looks like a rectangular piece of styrofoam to the uninitiated. I went back to find it and saw a lady with her kids playing as they walked the sand, picking stuff up as they went. She had a plastic bag and was carrying out the trash that people left behind. I asked if I could look in the bag and there it was. She thought it was a piece of beach trash... phew!
I now put my name inside my flyboxes just in case - although she probably would have dropped it in the trash can at the parking lot that day.