A small metal container used to carry booze. Also known as a "hip flask" to separate it from other types of flasks. A typical hip flask holds about four to eight ounces of liquor.
Using a flask is a decent way to drink in public if you're an old redneck at a Garth Brooks concert, but it's a pretty stupid way to drink in public if you want to drink while walking around a city or riding a bus. A soda, sports drink, or milk bottle with dark colored plastic works far better.
"There were a lot of flasks with Hammer & Sickle emblems at the gun-show this Saturday. Too bad I'm 2 years shy of being able to drink. Plus if they saw the Hammer & Sickle I'd instantly be labeled a commie. Damn prejudice."
-me
"...and then you'd just have to sit there and imagine why on earth you can't get ye flask! Because the game certainly isn't gonna tell you. And you don't have any of those precious graphics to help you out, either." -Strong Bad