Among the many things you generally don't need at the beach are a wallet and a purse. Leave those locked up at home. Stuff some cash in the zipper pocket of your bathing suit. Worst case, it gets a little wet. It'll dry ... and it'll still spend.
A cell phone is good to have. If you can't lock it in a glovebox, take it with you. Put that and whatever else you need in a light daypack.
Then, leave the car *open*, not locked. That way some moron won't smash a window, which usually costs more to replace than whatever they stole. I once had somebody in the US smash a $150 window to steal half a handful of small change. Grrr.
Just leave the keys with the car, lightly hidden if you like. People don't steal cars here as they have nowhere to go without getting caught. (Except those "hot-wire" teens at Point a couple of months ago. And, of course, they got caught.)