Ten points Peter!
Got an e-mail from a complete stranger who saw this thread on Mudcat (We really DON'T know all the folks who lurk here!) telling me about a little invention he came up with.
Three flat sticks, One the length and width of a small guitar fingerboard, one, a mandolin, and one a five string banjo. He's affixed the appropriate number of strings to each (I don't think they're tuned or anything...just screwed in)
Uses them on plane trips or in front of the tube, to practice on. I asked about "frets" and he says he just draws them on with black felt pen. Good invention.