There are a lot of festivals in Brittany this time of year.Probably already started.Some of the musicians taking part you will find playing in the bars and cafés afterwards.Something informal usually happens,way into the night most times.You could sit in,as it were.Also,you will find that in some small towns,villages etc,that there will be a Fête going on,with BBQs and roast whatever being prepared,could be a good place to set up.As to what to sing....just go with the flow!Just do what you do best.
May see you there!
Good luck

David