As Dave stated, the gratuities cover your dining room and Stateroom Attendant teams. They do not cover the automatic 15% gratuity that is added to bar drinks.
As far as beverage packages,
here is a link to the dining section on Royal Caribbean's website. Just click on the tab that says "Beverage Packages." However, in order for the soda package to be worth it, you'd have to drink at least 3 glasses of soda per day for that to pay off. They do have bottled water packages as well. I bought one of these packages on my last cruise, but I forget how much I paid. I think I was figuring 1-2 bottles per day in port, so I probably bought the smallest package (I think it was 8 bottles?) In order to purchase these packages, you must log into your reservation.
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2007 - Majesty of the Seas
2009 - Enchantment of the Seas
2010 - Freedom of the Seas