Get a big group of people and go as all the things Mark Sheppard has ever been.  There’s a good twenty costumes right there.

Better idea:  carry around a giant bag o’ Mark Sheppard costumes, and be a different character every hour.  Romo Lampkin?  Bring a cane.  Badger?  Nifty bowler hat plus tie.  Crowley? A hellhound (i.e. an iPod making disembodied dog noises).