Something warm as the wind up there is always vile. I normally end up in jeans, knee high boots, shirt, jumper and a coat, either tweed or quilted, a warm scarf and if cold a warm hat.
But, I do tend to wear the above for most occasions even on Gold Cup day I don't tend to vary too far from that as to be honest it's a long day, it's comfortable and smart and half the time we end up walking home from the course as it's quicker than getting a taxi!
Tweed! Surely it's dependant on which enclosure you're in as if in members I'd have thought no jeans etc. long time since I went - 20 odd years ago, so things might be different now.