We are a family of four and we all have our own snorkel equipment. Got it from target at the end of summer on clearance. We throw it all in a duffle bag so it doesn't take up much room. Then you can just grab the bag and head out when in port. Then you don't have to worry if there will be rental equipment or not.
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