Bernard, I can remeer many occasions when I have arrived at a venue armed with one only one instrument for reasons of carrying them and have asked to borrow another for various reasons which include accompanying a song on guitar as I can do the piece better that way than with my tenor banjo which I am most likely to carry. Also I have arrived at venues, not realising what the type of session is, gone to a venue to check it out,...I played better a couple of years ago than I do now but as an example, if somebody had not been willing to lend me an instruent a guitar to do a song when I had tried to suss out what was going on to, I left the banjo with a friend while I took a look and enjyed it.
Later that evening I went to anther session in the open in the town (armed with banjo) and Chris Sherbourne and Denny Bartley who I have met before asked me (actually it was Denny) asked me to kick some life into the session for them and we had a great time. Never knew urine could achieve that.
Jon