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It is customary to tip the room service person for each delivery, but also note that RCI charges a delivery fee of $3.95 for room service between midnight and 5am and that includes the tip. For a breakfast delivery after 5 am I would give the crew member $3 at least. This is a very busy time for them and they don't stop moving for several hours as the breakfast orders come pouring in. It is a good idea to bring a good supply of dollar bills along on a cruise for this type of thing.