Hooray For The Freedom Flask [Video]
What an absolutely brilliant idea! It's called the Freedom Flask, and it's a seemingly flawless way to sneak liquor into an event. From the date on the video, it appears this product has been around for a little while...but I'm just now discovering it.
Once you have this thing on, the only hurdle left is the fact that it looks like you're peeing in your Coke (or other carbonated beverage).