OP, just to clarify, exactly which cruise were you referring to?
The only true “fireworks dessert cruise” is the one on the large ferry boat for MK fireworks - Ferrytale Fireworks with a full dessert spread and drinks, including alcohol.
The other two offered are not marketed as dessert cruises, and are in the private pontoon boats, one at Epcot and one at MK. You do get cans of soda, water, bagged chips & snacks.