Paul and Tracey,
Welcome to cruise-chat.
You'll always find coffee and tea available somewhere on the ship 24 hours a day, and when the buffet is open for whatever meal you'll be able to swing by and get juice, milk, iced tea, lemonade, whatever beverages they happen to be serving at that meal. Given the buffet seems to be open more than it is closed you can usually find something to drink without paying for it.
I personally think Celebrity is being quite heavy handed in their prices for these packages. Pay as you go is probably the best choice.