In my experience there's only two places that you can walk out of an establishment with an open container, Vegas and New Orleans. By open container I mean an open bottle of alcohol or a cup or glass. I'm sure there are probably other places but those are the two that I know of. Most other places don't allow you to take an open container out onto the streets with you. Many people don't seem to know this.
"Hey, the cups gotta stay inside."
"It's just water."
"Still has to stay inside, it's an open container."
"But it's just water."
"The cup has to stay inside. Not my rule, it's the city's." At this point they either take the cup back inside or I take the cup away.
Easy enough, right? Sometimes it's an argument but most of the time it's not. People don't understand that even though it looks like water it could be something else, like vodka and soda or something like that. People also don't understand the ramifications if they actually got stopped on the street for it. If they say where it came from then it could be bad news for the establishment. Fines are something we tend to try and steer clear from.
People also try to hide their drinks as they leave also. I've seen people slip their beers into their coat sleeves, put them in their back pant pockets, in purses, and their jacket pockets.
I even saw one guy put his rocks glass under his hat. The hat sat up high on his head and he was walking like he was stiff as a board. As he got closer to the door I put my hand up. "Hold on man, your hat's crooked." So I reached up and started to adjust the hat and he moved. The drink tipped over and he was covered in what ever he was drinking. I just started laughing and took the glass out from under his hat, put the hat back on his head and let him out.
If I spot someone outside of the establishment with a drink hidden I take it away. I walk up say "Excuse me" and reach in and pull out the drink. Then I turn it upside down right where I got. If the person is quick enough they don't get the booze all over them. If they're not then they get wet and smell like booze. I figure they won't mind if they get soaked. After all, they were trying to take it with them anyways and now they can, just not in the same way they were hoping to.
Not all places have a package license meaning that they can sell alcohol that you can carry out. Many of the places I've worked haven't had these licenses. So if they don't have the license you can't carry anything outside of it.
That's just how it is.