Well, after fighting back the urge to hide/panic/run (because man, is that mental image ever scary), I'd blow the whistle I have attached to my keychain, and start using my very Loud (and apparently) very scary Teacher Voice to give orders to organize.

... Unfortunately this technique has only worked before on first-year university students, so I'd be hoping to all the gods that they'd actually listen to me. ._.;; Ohhhh dear. I'm generally not very good at getting anyone to do anything, unless it's a room full of frightened freshmen.