@JoeCamel pretty much covered it. About the only thing I can add is that if you're talking about a drink from a sit-down restaurant that's in a glass glass, you'll have to ask for a plastic to-go cup to pour it in. They won't allow you to walk around the parks or CityWalk with a glass container.
Funny related story: The first time we rode the Hogwarts Express was from Hogsmeade to King's Cross. We over-estimated the length of the wait and suddenly found ourselves standing on the boarding platform with more than 1/2 full beers and an arriving train. Rather than chug, we just brought them on the train. We found it odd that no one said anything, and we thought we were rule-breakers who'd gotten away with it. Then, much to our chagrin, on our return trip we discovered the snack shop in the King's Cross queue that will sell you a full-sized British beer to bring on the train.
-Rob