If it's an Irish trad session then bodhran if you're a good, sensitive player and know the tunes inside out, otherwise forget it, especially shakey eggs and those sodding things you sit an and beat with your palms - how to destroy the subtlety of the music in one fell swoop.

That said, if it's not a trad Irish session and no-one minds then go for it but remember the melody players need to be heard. There used to be a session over the hill from our house where anything went, and it could be a wonderful, mad night out.