Paying for drinks with your room card, and then requesting a receipt from the server.
When we purchase drinks in bars and nightclubs, we offer cash to the bartender with our credit card information, and request a “tab” so that all purchases will be charged against this one account number as place on file. But as no such borrowing system exists in more casual dining establishments, those who wish to charge their drink tabs to future bills may do so by paying their bills with a hotel room key or room card given at check-in. This process is more formal than simply sending a bill afterwards because it means that you’re giving explicit permission before purchasing any of these items whether or not you have negative balances on your credit cards.