Coffee is a highly caffeinated beverage that may be enjoyed in a variety of different ways. Coffee is generally used to keep Agents awake and counter the effects of hangovers and Rhum. It has also been noted that coffee tends to make the imbiber hyper.
Coffee also has the interesting capability of moving someone "forward in consciousness" (ie, it makes you more focused). This is essential when one is trying to purposefully get somewhere in Headquarters and cannot distract themselves.
Coffee featured in the second Playscripte along with Rhum.