Chocolate is a much beloved foodstuff among PPC agents.
Chocolate helps to ease some of the pain of badfic, prevents attacks of Bloodwrath, and is handy when you've spent too long near Dementors because that damned Posessed!DarkLord!Harry Stu is living in Azkaban.
While living off of chocolate solely is generally not a good idea and Medical would likely suggest that you not do it, many agents try to do this.