What to wear
It's not the Oscars, so no sexy evening wear - you don't want to upstage the VIPs. Charles's coronation will be simpler than his mother's. He'll probably look more like one of the Beatles on the cover of the Sgt. Pepper album than a traditional monarch, dressed a bit like Father Christmas on his way to a drag competition.
Don't go mad when choosing your hat; the people behind you will be thankful. In the words of Jean-Paul Sartre, hell is other people. That's never more true than when they wear a big hat and sit in front of you. And if you're worried about going over budget with your outfit, wear something recycled. The royals will approve, and you'll be following Camilla's example: she'll be wearing a recycled crown.
Finally: avoid metal. You may have to go through a security scanner like the ones at the airport - so, save any medals you may have for another event and leave your official chains of office at home.