Here's a great instrument I use when I do gigs with different musicians I know just to mix up the show a bit. It's called the Stumpf Fiddle. They would make a great prop to bring around with you while at a city festival or music festival and (if it seems like it would be welcomed) join in the jam.
Here is a video of an explanation of the Stumpf Fiddle
Here is a video of it being played along with a song.
And here is a
link to a place that sells them if you would like a really nice one.
I make my own and you should at least try making one yourself before purchasing one. Making them is more than half of the fun!