Here in Canada it is still illegal to carry an open container of liquor but Im pretty sure we can carry a flask, but hey they meant to be discreet anyhow. The law, I find is pretty lax when it comes to open alcohol unless you are doing something with a car, then they throw the book at you. I remember my underage drinking days at bush parties. The police would just make us pour our beer out onto the humongous bonfire we always had and sent us away. Heaven knows how they ever found us!
I remember one time drinking in a parking lot across the street from a buddies house and the police stopping by, well I was leaning on the roof of the cruiser getting lectured about drinking in public... You see it was a hot day and my beer was quite cold and I just accidentally took a swig. Well the cop started cursing and swearing that he wasn't going to charge me but the least I could do is not to drink it when he's lecturing me. Well he probably laughed about it later but I don't know who was more shocked at my actions, him or me.
I certainly dodged a bullet that day, which up here is a figure of speech whereas probably down in Texas that's a statement.