Baby oil is great to highlight the face. Baby wipes are handy to have ring side for any quick fixes on you or the horse. Also a good way to quick clean the boots ring side. Hoof polish is a must. Always have a small sewing kit handy in case a button comes loose. Small mousse or hair spray to tame any flyaways on the braids.
ASsuming you've given your horse a bath and they are braided and trimmed etc etc, then keeping them inside a stall is the next best thing. Throw jammies on that cover the the head and neck to protect the braids and keep the horse clean, a cooler and wrap them up over night. The legs are easy to quickly brush off in the morning unless you own a grey then you are always at risk of having your horse covered in green regardless of how hard you try to keep'im clean.
Show sheen is alway a great product to put on the prior to a show as it helps decrease the chance of poo or various other things to stick on. Hmmmm....I think that's it for now.