If I'm staying onsite, I like to use my room key for larger purchases. But for just a pin or a bottle of water, I bring about 100 in cash. This way if I lost it, I wouldn't be out a whole lot. I also lock up all of my credit cards, car keys, bank cards, and extra cash in the hotel safe and only carry what is necessary. I know some folks say the room key is easier, but when you're waiting in line, to pay for something that costs 3.00, sometimes it's just easier to give them the money. I carry a lot of singles too, so I don't have to wait for change.