FWIW (For What It's Worth..) seeing this thread is less than serious

I wear..
1) Loose fitting cotton t-shirt (but not so loose fitting that you can't show off your six pack to suitable persons at arrival airfield).
2) No baseball cap or hat. Only chavs wear caps (normally whilst speeding in their Vauxhall Corsa SRi).
3) Light denim jeans or lightweight "North Face" type trousers (they help to preserve the curves but avoid making you look like a Royal Mail postage sack..).
4) Trainers. As much as I detest them they do help to give more feel through the rudder pedals and help to prevent catching toes on the brakes during takeoff...
and finally: NEVER WEAR ANYTHING WHITE! IT WILL BE FILTHY AFTER THE "A CHECK"