What show are you going to? (I am in south texas and will be going to waxahachie next weekend so just curious!)
To prepare make sure your rabbits are all tattood. Groom any rabbits if you need to either the night before or morning after check in. It really depends on what breed you have. If it's an early breed there is not much time to get ready before they start calling the breed unless you get there early. The night before you can also clip nails. Judges really appreciate this. We fill out comment cards before hand because we have them at home. If you don't have them at home the show should have some by the check in table. Print out directions to the hotel/showroom or at least have the address on hand or already programmed into the gps. Also we print the show flyer and bring it with us. Normally shows will link a copy to the entry form to the flyer so print it out and fill it in before hand. If the show doesn't have it you can try looking on rabbit websites for an ARBA entry form.
As far as buny supplies we have a lot on hand. Hay, pellets with the mixings, water, the pedigree book, nail trimmers and quick stop, something for grooming (carpet or the table), brushes, pens, sharpees, tab ointment, benebac, and electrolytes. Some people take disinfectants to shows so they can spray their carriers or the judging coops.
Normally at shows there are vendors that you can purchase supplies from if you forget something. Oh and the night before we make sure our carriers are clean and filled with wood pellets and PDZ in the bottom on top of puppy pads. We also put a little hay in there