Here’s a simple little hack to keep your things safe on the beach from prying eyes that I’ve seen using a wide type of sunscreen bottle like this:
You’ll want to keep things like you’re keys, money, etc., but, the opening is usually pretty small:
so by taking an Exacto knife and cutting away the top except at the lip where it can still attach at the original top:
you can make a wide mouth safe to put your stuff in that nobody will suspect.
If you have trouble keeping the top on, just use a hair elastic, no one will think anything of it: