Sneak-It-In Disposable Flasks
Since flasks are generally metal and not pliable, these disposable flasks could be useful if you really must bring your whiskey with you. I don't actually drink much booze, but I can see myself sneaking espresso shots into the Coachella Music Festival (where they don't allow bottles or beverages from outside of the event). And, come to think of it, if you put hot beverages in there, it would be like a hot water bottle. I ice skate during winter, so hot cocoa (and maybe even spiked) would serve dual purposes!