Its hard to determine how much to tip the server when the food doesn't cost anything. We typically give $3 to $5 for a full room service meal. But coffee and toast or a desert is a $2 to $3 tip. If they are on time and the food is warm, then a higher tip is proper. Just remember to order in advance.. Especially for breakfast. There are a large number of peopledoing room service breakfast and they get backed up quickly if you don't put you order in the night before, then you may not see your order come for a long time. Nothing is worse than sitting around in the cabin waiting for you order to come when you could be out enjoying the ship.
IF you plan on making it an everyday occurrence, consider giving the waiter a larger tip than you think is warranted the first day while mentioning that you plan to order you toast and coffee each day (or each sea day) and that you appreciate their prompt service. When they know they are going to see a tip they tend to work a bit harder for a person.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013