For the benefit of those of you who walked in, after the movie started, there is a law in most states commonly referred to as “the open container law,” and it pertains to open bottles, cans, and other containers, which have alcoholic beverages inside. A bottle of beer, wine, or other spirits, which has had the “seal broken,” or which has been previously “opened” is considered an “open container.” So, if you have filled a flask with anything that is alcohol in nature, it would be considered an “open container.”
If you are going somewhere, and you want to bring your booze with you, it is a great idea to keep the flask in the trunk of the vehicle, because when it comes to driving, the “open container law” does not usually apply to what is in the trunk. There have been people pulled over for something like speeding or running a stop sign, and they were on their way to a recycling center with a back seat filled with soda and beer cans, and they could have technically been charged with violating the law. So, even a bunch of empty beer cans or bottles, should be transported in the trunk.
Laws vary from state to state, and it is best to check with the laws in your state, or county, to be sure you do not bring a flask to a public place or an event where alcohol is not permitted, or where “open containers” are forbidden. But your flask is certainly an open container, even when the cap is securely on and fastened. Always use good judgement when drinking, and when carrying your favorite beverages with you.
During prohibition in the early part of the twentieth century, flasks were commonly used to discreetly hide and carry alcohol, as well as drinking it discreetly. These days, they are simply a convenient way for someone to bring their favorite spirits with them. As an example; dad is going to a wedding where he knows they will have beer and wine only, or a limited selection of “bar brands” or “well brands,” but he prefers his 15 year old, single malt Scotch, so he brings some in a flask!