They provide shower gel and a "shampoo/conditioner". If you must have your own seperate conditioner, then you should bring a travel sized bottle of it with you. We bring a "scrubby" to use with the gel, they pack easily. I've even seen people tie the scrubbies (all one color) onto their luggage for quick ID at the airport and then us the scubbies for the cruise and then tie them back on for the return trip....
They also put a "gift basket" of various samples in each bathroom. Stuff like BIC razors, hand lotions, shaving cream, toothpaste, etc.. although the items in there are probably marketing related and will vary from cruise to cruise.
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