Drinking and driving is illegal and dangerous. You know this. But what about having an adult beverage present in your car while driving? Well, that becomes a little more complicated.
The TEA-21 Act prohibits the consumption or possession of alcoholic beverages in a vehicle while driving. But many states don't comply with the law, or enforce a more extreme version of it. Needless to say, this is the kind of thing you might want to familiarize with, lest you get fined for someone holding a beer in the backseat.
Study up: Hands on the Wheel: Get To Know Your State's Open Container Laws.