Beverages are included at mealtimes. (Topsiders buffet has fruit punch, tea, coffee and milk, but no soda.) Soda is available (in addition to coffee and tea) in the dining rooms.
A soda 'sticker' is available for purchase (35.00 for a 7day) that permits unlimited refills for the duration of the cruise.
I haven't cruised this year yet, so I can't be exact about the above price. I've also heard that the 'soda mug' is an optional purchase now. Sodas are available in all bars and Pluto's dog house and Pinocchio's pizza.