I tie the lanyard to the 'string' of my bathing suit, or a belt loop or 'something else' and stuff the holder in a pocket most of the time, and INSIDE when swimming so it won't float away.
bought both on
DCL . . . red has Castaway logo (bought on CC obviously), blue has DCL logo
still sold ... commonly seen in beach stores, surf shops, dive shops ...
I just noticed a name molded into the bottom of one and found:
http://www.witzsportcases.com/travel-resort-cases.html
"Witz waterproof ID and Badge Holders are perfect for carrying drivers Licenses, TWIC cards, photo IDs, credit cards or any other forms of ID. These cases are made of crush resistant ABS plastic and have rubber O-rings to keep out the water and dust. These cases come with a neck lanyard and Carabiner. "
My small (blue) one easily holds a ship key card, a credit card, and a photo ID and a few folded bills. The larger red one can hold up to the size of a pack of cig's ... I don't smoke, but if you want to carry more it is available.
They also have a passport sized one, smartphone and eyeglass/sunglass cases.