I usually wear the same clothes, but they are the clothes I am normally wearing anyway. I don't get changed specially. What I do on the day depends on what else I am doing. There usually isn't time to think about it.
Tomorrow I have a meeting at 11 and another one at 2, I have to print some posters and deliver them to where they are being displayed, I have to go and pick up something I bought from eBay, and I have to send a registered letter to Luxembourg.