Hello Maria,
With the Disney Dining Plan (DDP), each person will receive a non-alcoholic beverage with their meal. From my experience, this includes soda, coffee, tea, juice, milk, and bottled water. Some restaurants have allowed guests in the past to have a smoothie or a milkshake on the plan.
Not included on the DDP are alcoholic beverages, some bottled drinks, and souvenir drink mugs.
If you find a milkshake you really must have, inquire about using one of your snack credits towards it.
For more on the DDP, click
here.
Hope this helps!