Keep in mind that we are there to find stuff LOST by others. And much of the good stuff we seek is lost IN the water, as opposed to on the beach. Now, before someone hollers about it, some items are lost ON the sand/beach itself. Any ONE thing can be any ONE place. But it's the odds of recovery which tip in our favor that we must concern ourselves with first.
Next time you're at the beach, WATCH your fellow frolickers for awhile. "Objective People Watching" is a habit you should cultivate anyway, since that which we seek is deposited where we can find it by others.
At the beach, the good many folks who are there to spend their time on the beach, take pains to secure whatever belongings they might lose BEFORE heading to the waterside. They are more staid and predictable folks, as a rule. My wife is a good example. She is there to sun and relax, with only occasional and cautious forays into the water. Most of her jewelry is in her purse in the car long before she hits the sand.
Many others are just like her, Ive noticed - maybe the maojority, in fact.
Its those reckless spirits who do not take such pains that we are interested in, and there is one primary lure for them: THE WATER. This includes the younger folks (or the young at heart), studly blokes posturing for the ladies and the same hotties, sporting about for those self-same studs. They leap to the water with abandon, run and splash and wrestle, diving and splashing around like otters at play. These are the folks to watch the most. Where do they jostle about the most? Where do they "hang out" the most?. That is where you will soon find yourself, if you are astute.
There are some likely spots ashore, to include volleyball areas, the shallows where kiddies and mommies scamper, changing/shower areas (as already noted) and traffic funnels.
The beach itself, as a whole, offers a proportionally greater chance at potluck, unless you can narrow it down to "Activity Zones."