Tack: Saddle, bridle (nice one's) girth, nice fitted white saddle pad, any kind of boots you use, breastplate (if you use one), also bring a extra saddle pad or anything that might get dirty and you can use it for practicing!
Show clothes: Helmet, hairnets, spurs and crop, show boots, paddock boots and half chaps (just in case) gloves (if you use them) riding jacket, show shirt, show pants, socks (i forget everything so I bring extra)
Horse clothes: Travel boots, fly mask (Sometimes needed), cooler
Supplies: fly spray, grooming supplies, hoof polish, all your brushes,show sheen(not always needed but..) little clippers for touch ups, lunge line and whip, waterless shampoo, halter and lead rope a nice and ugly pair, sweat scraper,braiding elastics or thread the color of your horses mane, leather wipes or cleaner, wash bucket (always needed), rags,sponges, mane and tail detangler, braiding comb,
Feed: Hay, Feed buckets, water buckets (usually two), treats
Stall: Forks, broom, stall guard and a tying rope.
Here is a couple tips!!
If you own a mare wash her milk bag before doing any class (some judges check for that) And around he or she's dock and eyes!! :)
Also bring a lint roller (it is VERY useful)
Just one more thing... OVER PREPARE if your doing hunter (as in jumping) practice any pattern that comes to mind, also if you think of something extra that could be useful DO IT some judges give you extra points for extra good appearance!! :)