I looked up the restrictions for the Carnival Cruise line.

Items not allowed on board:
Knives longer than 4in (dive knives can be stored with security officers)
Scissors longer than 4in
Fire Arms, spear guns
Tasers / Mace
Ham radio equipment (this one really amazed me!)

More info can be found here: http://www.carnival.com/CMS/FAQs/What_NOT_to_Pack.aspx