Haven't done the cruise yet, but was successful in getting a reservation, and people have kindly responded to my questions about this. There are cruises for both MK and Epcot fireworks and daytime cruises. Dial the # about 2 minutes before 7AM at 60 days before the date you're looking to book. If you get the "we're closed" recording, hang up and hit re-dial until you finally get through. Do a practice run, so you know the buttons to hit ahead of time (you're asked 4 questions before you finally get a CM). Once I knew the drill, I could punch the #'s in without waiting for the spiel.
Talk fast --- "Pontoon boat for Illuminations cruise on April ........."
I booked Illuminations cruise, so didn't ask questions about MK. There are 4 pontoon boats, which seat up to 12, plus the Breathless, which seats less, but is a gorgeous speed boat. Before I caught on to how to time the phone call, all boats were gone by 7:01. The pontoons are $120, plus tax, plus driver's tip. Breathless is $180 plus tax/tip.
The official word is that you can't bring food/drinks onboard, but several people responded to me that it's up to the driver, and snacks and beverage would probalby be OK (no coolers). The driver has to clean up afterwards, so slobby behavior isn't appreciated and an elaborate picnic doesn't sound like it would be allowed..
Disney will provide deli sandwiches and drinks, but the cost is $20 pp (minimum of 4), and it costs more for cheese/crax, dessert, alcoholic beverages. Cruise is non-smoking.
I was given a choice of pick up at Boardwalk or Yacht Club and told to be there at 8:15. If Illuminations isn't a 9 PM, the cruise won't include that --- it's just for 45 -60 minutes. A credit card was taken to hold the reservation, and we pay the driver when we get there. Cancellation is 24 hrs in advance. The boat rides around the lake a bit and parks under the bridge by England. I'm mildly apprehensive about the wind blowing in the wrong direction and all the smoke from the fireworks would hit us --- this could happen, but apparently not very often. Guess it's a gamble, and I'll be optimistic.
Good luck!