Thankfully, Southwest hasn't started charging for bags yet! I always try to book with them; it's waaaaayy cheaper.
Anyway, if you plan to bring wine/champagne on board (you are each allowed one bottle in your carry on boarding the ship) then don't forget the wine opener.
Also, I packed ear plugs because my boyfriend hates the constant morning announcements. Seemed to work for him. I'm always up early and couldn't care less about the announcements.
Lastly, my iPod with speakers (Walgreens sells them for $10). When we're in our room getting ready for dinner, or hangin late at night, we always have the music on!
Enjoy your cruise!
Carnival Inspiraton, Feb 2006
Carnival Glory, Aug 2007
Carnival Liberty, Aug 2009