The casinos in Las Vegas are designed to keep you gambling as much as possible. This is true on a large scale - the buildings are designed to keep you inside. The gambling areas have no daylight, so you have no sense of time, and the exits are deliberately hard to find, so that you wander around inside the casinos for as long as possible. But this dedication to keeping gamblers at their posts goes down to the little things too.
So, you're playing the slots, and you have your special plastic cup to keep the coins in, as you put coin after coin in the machine. Handling all those coins will get your hands dirty. No need to go wasting time washing your hands - just pick up one of the complimentary 'towelettes'!
Not that I did very much gambling, really. It's not really my thing, and there were so many other things to do. A lot of shopping, for a start. Here's a gambling souvenir I couldn't resist - one of those 'lost in translation' things.
And in case you're wondering why they're giving you the obvious information that 'Dice are not edible', those are chocolate (gambling) chips!