I am training towards eventing, but mostly do dressage. I don't really show a lot, but I always have EVERYTHING in my trunk just incase ;)
On the front left, I have my huge grooming bag (3 curries, 1 hard brush, 1 medium brush, 1 soft brush, face brush, super soft show brush, hoof pick, corona ointment, swat, fly spray, marigold spray (shiny), avacadoe spray (tail), gel (super detangler), body brush, fleece mitt, two kinds if mane pullers, quick trimmer... I sure there's more in there)
Back left, gullet plates for wintec, a girth thrown in the back, trash, saddle conditioner, cleaner, and rags
Top right, bucket with three shampoos and conditioners, two special scrubbers, and a sweat scraper.
Back right, four pairs of polos.
When I go to shows, I throw a bag of peppermints on top and his splint boots.
I thrown my numerous saddle pads and half pads, and saddles in the back if my truck. I usually print the horse show checklist off of thehorsechannel.com for all my stuff. I put my show clothes in a garment bag and hang it up in the car.