for showing, other than a show quality rabbit, you'lre goign to want to keep the grooming up, like the others said, but also their nails. Iv'e run across a few judges that actually over looked a rabbit with longer nails for one that had shorter, neat kept nails. Keep your tattoo's neat, clean and clear, or be prepared to pay someone to put a tattoo in your rabbit's ear. YOu may or may not find anyone that will/can do that so making sure it's done prior is much better.
Leak proof bottom show carrier is required at most shows. I would suggest bringing a chair for the show, a couple of towels, a small spray bottle with cool water, your own snacks and snacks for the bunnies. My bunnies won't eat food at the show, but will munch a little bit of an alfalfa cube- comfort food I guess. Keep a check on their teeth before hand and good clean tattoo's. I also bring a camera with me. I try to take a few pictures of the show room, for personal means, I just like to do this, it's completely personal but I will modify the picture to blur out any human faces. I will sometimes bring a book/ drawing pad or something with me for between shows, I let the bunnies have soem down time between shows(Double show days) to just relax and hang out in their carriers. I also have harness' for my buns, I bring a couple wiht me so if they want to get out, I cna take them outside to hop in the grass near the showroom. I have brought my laptop and my pedigree book with me if I"m selling any. If you are selling any, bring the pedigree's of the ones for sale, all printed out and ready to go. ALso bring small bags of grain for the sale rabbits so they have transfer food.
As for food, my guys are doing great on Purina Green bag(or pink right now) and they also did great on Manna Pro- Pro formula. Both of which I get at Tractor Supply company.