I've some mates that do that on long rides. It works well - they just keep a separate camelback to eliminate nasty beer aftertaste. You should know that this probably violates more laws that simply DUI - having an open container is illegal by itself, even if you aren't drunk.

As for beverages of choice, a flavorful dark beer is usually what I'm after. However, as someone else pointed out, ice cold is not the way to enjoy beer. When it's hot out, my (post)ride libations generally center around gin. There's nothing better than an ice cold gimlet in the hammock on a hot day!