Well I was speaking in fun, but actually for me it depends on which setup I'm using. At my rehearsal space I'm typically using my old Crate combo, no top vents or anything plus it's an inexpensive pawnshop item so yes I usually have a beverage along with songlists, tuner, and sometimes a laptop.
My Peavey head has top vents, so no beverages on the top of that one.
Also probably geeky, but you'll find me drinking coffee 9 out of 10 times at my rehearsals, only the occasional beer and that's usually only if our rehearsal has a guest guitarist or keyboardist (got some good local talent that love to drop in and play some blues) and instead of working we are doing more of a jam.