I need a "toy" for DS's Christmas stocking... 
It is a family legend that I always put something in the DC's stockings that I knew would keep the recipient amused on their own until lunchtime. It started as a way of keeping the DC occupied until we opened tree presents in the afternoon but now, even though it is entirely unnecessary, we still keep up the tradition. It's fun to have something to do once lunch is prepared and cooking.
But I have run out of ideas for DS this year. We've done a lock picking kit, a suture practice kit, a magic trick and a human anatomy colouring book in recent years. It needs to be something for one person, as the whole point is it's something to do in a quiet moment when everyone else is busy. Not a book (they get a book too) and not a jigsaw. Some other kind of puzzle or something small to construct could be good. Extra points if it has something to do with guitars or medicine!
Anyone have any suggestions?