Wear what fits with the style of music or occasion. Number one rule is not to look like a shile of pite. People may have paid money to see you. Make a bit of an effort to entertain them.
Many years ago a fellow band member had been building a fireplace and came straight to the gig without changing. Imagine the love child of Compo and Selwyn Frogget on guitar and you'll get the idea,
Not good,