When I worked at a truck stop I never charged emergency personnel (police, fire, etc) for coffee. Some insisted on it. When I did a brief stint filling in for an assistant manager for another site, it was close to a military base, and started doing the same thing for buses full of soldiers on training breaks, until one of the DI's requested that I charge them.
Times change, I suppose.
I am thinking about doing this next year though. I'm probably going to want to pick up a Kelley mouthpiece beforehand.