Because I tend to go to events on my own I try to do as much preparation in advance leaving as little as possible to do at the event itself.
Something that takes surprisingly long especially if you have limited or no living space in your lorry or trailer or alternatively you have a horse who doesn’t like waiting about once ready, and getting changed into your show gear.
Obviously you don’t want to risk your breeches getting dirty either so the easy solution is to have a trusty pair of ‘over trousers’ which fit over your breeches keeping them clean and you can whip off quickly after getting horse ready at the last possible moment.
Personally I have a pair of lightweight jeans a size larger than I normally wear which are not restrictive and not too heavy so I don’t overheat. Waterproof trousers work just as well but I get annoyed by the rustling and they can make you get hot. Tracksuit bottoms also work equally well as jeans and are looser fitting normally with an adjustable waist.