My favourite folk instrument, by a long chalk, is the fiddle. Having said that (thereby sticking to the sentiment of the thread as I thought I understood it), I confess to not knowing one end of a fiddle from the other. I can play only one sort of instrument and that is the harmonica, though I do play three iterations thereof, namely blues harps (which I retune for the ould jigs, reels and polkas), chromatics (when I'm forced to) and tremolos (far more these days than I used to play them, in order to blend in with my Cornish singing band).

If I had to pick just one to take to the desert island it would probably be a Tombo Band 3121 tremolo in the key of G. I might just try to sneak in a Special 20 low D* down the front of my shorts and pretend I was smuggling a budgie...

*You can't get these any more, but I still have a precious few from days of yore.