I can back up the story that the onboard referigerators will take for ever to chill any drinks you bring on board.
From my experience, I would suggest not taking any extra food on board (there is plenty of free food). But I would also recomend bringing some of your own cans of soda/pop/coke to keep in your room.
Unless you purchase the special mug (which I seem to recall is somewhere around $30, someone please correct me), every time you want a drink, your going to have to pay for it except at scheduled meals. For example, if you go to Pluto's to get a burger and fries, they don't have drinks. You have to go across the way to the bar and PURCHASE as drink to go with your burger.
The first time we sailed (just a few months after the Disney Magic was launched), getting ice in our room was near impossible. But since then, Disney seems to have gotten their act together and we always has ice in our room. It's been great that any time we were sitting in our cabin, we could get a soda poured over ice without leaving the cabin or having to pay extra.