OK - dress informal, but if you have a MudCat T-shirt you could wear that for solidarity's sake! Have a beer or two handy to lubricate the odd chorus.

I once heard Peter Bellamy do a storming version of "My Way". Being Peter, he had "personalised" it to the point that he was halfway through the second verse before most of the audience realised what he was up to! His version of "Amazing Grace" was pretty amazing, too.