Are you taking part or going to watch? Either way, traffic builds up very quickly and can be a nightmare. Usually plenty to see - the usual stuff that is it most county shows, main ring displays, hunter breeding classes, dray horses etc
I go every year and if you like county shows then you'll love it. I always go around 9.30 and although the traffice gets quite bad the longest I've been in a traffic jam is about 20 minutes so thats nothing compared to going to the Great Yorkshire where I was queuing in the traffic just outside the ground for one and a half hours! If you go later on in the day the traffic may be much busier.
There's plenty of horsey things on the go - working hunters, mountain and moorlands etc and also heavy horses. This year the main attraction is Cossack riders which are always fun to watch!
Have fun and go early enough to avoid the traffic.