I wore my normal going out clothing i.e.casual/smart, out of respect for the panal, and of course my own self respect; Wear what you're comfy in as long as it's clean. The panal will take notice of what you're wearing, so make sure it represents your claim! Good luck
It's good to show some respect for the Tribunal, but don't forget that for IB you score a point if you do not care about your appearance and living conditions!