at the deck 9 drink station you can get (at no cost): filtered water, coffee, tea, juice, and I think (maybe) lemonade. Soda is free at sit down meals, otherwise you have to pay for them (including at the buffet).
At the drink station on Deck 9 there is coffee, tea, milk, ice tea (unsweetened), lemonade, fruit punch, hot chocolate. I think that's it. In the restaurants all drinks are free except anything w/ alcohol. Room service you pay for alcohol, soda and bottled water.
All the drinks that the others have mentioned are free. You also have to pay for Lemonade at Room Service only, it's free on Deck 9. If you have kids, you will always be hit up to get them a smoothie which cost. And anything that contains alcohol costs.
It may be worthwhile to bring a decent sized mug or two along that you can put in your room "fridge" full of lemonade or iced tea, free from deck 9. The deck nine drink station can be quite a haul from a cabin forward on a lower deck.
They also sell bottled water for the excursions.
Disney generously allows you to bring your own beverages (alcoholic or not) on board (most cruise lines don't officially allow this) as long as you carry them on board (not in your checked luggage, where an exploding can or broken bottle can ruin all your clothes, and the clothes of the person with the suitcase under yours. And not, IIRC in a cooler).
Fruit punch was available on our Wonder cruise - but its apparently hit or miss as to if it is there or not.
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