Found this on the beach in NJ yesterday. Now don't laugh, but you have to pay to get on the beach here in the summer. Most towns give you a beach tag or a beach "badge". If you aren't familiar with a beach badge, it is a thin piece of plastic, I'm guessing vinyl, about 2 inches square. They are dated of course so you can't use them next year.
Take a look at this one; it is 27 years old! There is no telling if this was in the ocean for 27 years, or if it spent some of that time buried in the sand. Maybe it went a few hundred miles south during a Nor'easter and made its way back. Maybe it did that ten times. Maybe it circumnavigated the entire North Atlantic. Belmar is two towns away from me, less than a mile.
The point is that besides being a bit faded and a little bent at the edges, this little piece of plastic is entirely intact 27 years later. We all pick up our share of plastic on the beaches; rarely is it dated. Makes me wonder how old some of the other stuff we are picking up is.