There are usually plenty of hangers supplied in the closet. They're just basic wood hangers, probably about 10 - 12 per room.
Majesty of the Seas - 10/03 & 02/07 & 11/08
Enchantment of the Seas - 10/04 & 10/11
Mariner of the Seas - 10/05
Vision of the Seas - 10/06 & 09/07
Carnival Liberty - 10/07
Adventure of the Seas - 9/08
Ruby Princess - 12/09
Voyager of the Seas - 9/10
Carnival Spirit - 11/10
We always throw a few of the wire hangers in, just so we don't have to wait to get things put away in the closet on hangers. A few things we just put on the hangers, fold them and lay them in the suitcase. When the suitcase gets to the room, we just pull them out, already on the wire hangers and stick them in the closet. Nice!
I like to bring a hanger or two. Mostly because I like to hang my clothes while I steam them, and I hate those nubby hangers with no hook, that most hotels/ships have (you know, the ones that fit on a groove that hangs on the rod).
Disney Fantasy - 2013 [pending]
Disney Dream - 2012
Royal Freedom of the Seas - 2011
HAL Eurodam - 2011
Royal Grandeur of the Seas - 2010
Carnival Dream - 2010
Grand Princess - 2002
Royal Voyageur of the Seas - 2000
Royal Sovereign of the Seas - 1999
Carnival Ecstacy - 1991