I was looking for milk at the DLH last month. All I could find in the gift shop was the little cartons.
On past trips, we have stayed offsite and gotten at least a quart, if not a half gallon, can't remember for sure, at the gift shop in the Tropicana Inn. It's so close, that you could take a walk over there to get your milk. The Tropicana is right across the street from the main entrance. Walking from the DLH, go past the entrance to DL towards the Lion King parking shuttle. Exit the resort, cross the street, and Tropicana is 2 hotels down on the left. There's also a Denny's, IHOP, McDonalds, and Mimi's Cafe right out here, so it might be a good lunch trip. Just stay away from Capt'n Kidds.