Going back about 40 years it has always been the case that guys who are on the shore several nights a week carry everything with them and leave the doors to their empty vehicles unlocked. Don't know how that evolved as what was considered the "best way" to handle the problem but I can remember very clearly several old timers telling me that was the way to do it even 4 decades ago.
Now it does have its draw backs. I once came back and found a guy sleeping in my car.
I also came back one time to find someone had puked in my car. Yeah , that's nasty!