Princess Steph
I'm sorry I don't know about the milk. They do sell small milk jugs in the food court which is across from the gift shop. It's open late too, so you could pick a jug up on your way from the bus stop in the evenings and put it in the ice bucket until morning.
That's what makes this resort so great is how easy it is to get around, especially with kids. Each morning it was fun to go down and bring back breakfast to the room for ds and dh. 2 bagels (which were huge) 2 cups of fruit and a juice or a milk came to about $12 if that helps. I had packed water, sodas, cereal and granola bars, but we took most of the food home...vacation mode I guess, LOL.
Oh, and if you'll have a car, there is a Hess station on property close to the resort that might have convenient store stuff and then Goodings is close by, straight out the Disney entrance into the shopping plaza where there's a Perkins and a McDonalds.
Hope this helps a little. Have fun.