You will need this stuff, I think.
A shirt like this one, you can get short sleeve ones but long are better RJ Classics Essential Ladies Wrap Collar Show Shirt - Sale - Show Shirts from SmartPak Equine
You will need beige or tan breeches I think There might be a few other colors. These are the ones I have they are really good. Tuff Rider RIBB Low Rise Knee Patch Breeches - Knee Patch Breeches from SmartPak Equine
You will probably need field boots you might be able to get away with some nice clean half chaps if field boots are too much
As far as jackets go I think the best colors are blue, gray, green, black I am not positive on that though. Equine Couture Raleigh Soft Shell Hunt Coat - Soft Shell Jackets from SmartPak Equine
You also need gloves mostly black are good
You will also need a helmet of course
If you don't have a show helmet then you can get velvet covers that make them look better sometimes.
For your hair if you can put into your helmet if you can if not you can do a little bun thing just at the base off the helmet. You can also put a hair net the same color as your hair on to keep the fly a ways under control.
I think I got everything, I have not shown in two years so I might of missed something. Do look around a lot you can probably find most of this stuff for some good prices it you look hard enough.
Good luck on your show I hope I have helped!