The plastic bag, usually from a local grocery mart, that is used to carry you beers around in. This is usually due to the fact that you ahve placed all of your beers into your refridgertor, and have thrown away the box. When it comes time to take the beers with you to a party you put them into a Puerto Rican Briefcase.
Wow, you have four different kinds of beer in your Puerto Rican Briefcase. Cleaned out the fridge tonight eh?