Um, really? Go to the restaurant and purchase a giftcard, put it in an envelope, put a stamp on it, write the recipient's address on it, put it in a mailbox, and that's all there is to it!
Joe has it. It's, funnily enough, not that unique of a question. Simply ask the hostess, host or waiter for a gift card or certificate and they will find what you need. :)
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