They are usually called BUNGEE CORDS.
There are not enough collectors to make them very valuable.
They can be useful for trading for other casino collectibles.
Check e-Bay for prices of recent auctions.

I throw away the cords and keep the clips (BUNGEE CLIPS) only if the casino name is on it.
I would sell 25 different clips for $10 plus postage, 100 different for $35 plus postage.