civil war jamming?

If you have ever played in a jam with civil war/minstrel era/Stephen Foster buff players or reenactors... how have you adapted to fit in?  What key whistle seems to be the go-to practical key for tin whistles in that setting or in that repertoire?  

What must one take into account in terms of authenticity, weather, adapting to the other musicians on other instruments.. ?  Any tips you can share for playing whistle with civil war buff musicians and repertoire?