The cruise line suggests a "reasonable amount". I've personally never brought more then one bottle of water on board because I think the water on there is better then anything I've picked up in a bottle. I don't know how much pop you drink but the most I've seen people bring on is one case period.
Life is too short to let the ship of your dreams sail without you.
Carnival Destiny Feb. 2006
Carnival Fascination Feb. 2007
Royal Caribbean Grandeur of the Seas Feb. 2008 The DTW & MsBJ tour
Carnival Valor MsBJ and Dina Feb. 2009
Carnival Glory MsBJ and Dina Feb. 2010
Carnival Dream MsBJ and Dina Feb. 2011