Welcome to Cruise Reviews, Sian_Eliza!
We are happy you decided to join us and ask your questions here. Lots of Royal Caribbean experience to be had here. It is my favorite cruise line.
The pre-paid gratuities you paid cover your dining room tips and cabin service. They do not cover the automatic 15% tip added to each bar order, and bar orders mean anything you order as a drink at a bar. This means booze, soft drinks, and bottled water. Yes, bottled water is not free. I think it is around $2 for a liter bottle. You can order a water package which saves some money. They also have a soda package and a juice package. They do not offer alcohol packages for cruises from U.S. ports, and even then the alcohol packages are only on a couple ships right now. A Guinness will cost around $5 or so. A glass of wine will run from $5 to $10 or more...it depends on the wine. Cocktails will run the same price range as wine, again depending on what you order. A rum and coke is $5.75 before the tip is added. A martini made with high end booze will be $10 or more. Remember that they add that 15% to the tab automatically. This is standard practice for all mainstream cruise lines.
I am a huge supporter of using the ship's drinking water and not buying it in bottles. The ship's water is tested for bacteria and other bad stuff and it is all I've ever drank (well, when water was what I was drinking!). Just remember the ice cubes are made with ship's water, so you can't escape it unless you like unchilled beverages.