There are going to be germs floating around and on surfaces but as long as your rabbits don't get an infectious dose their immune systems should be able to handle them
Make sure all show rabbits are in good health, try to minimize stress (ie by practicing going on car rides and being handled/posed by strangers), don't alter their diet (stick to pellets and hay - NO treats!) bring water from home, change soiled bedding frequently, have a plan to keep them draft free, dry and/or cool (or warm) - buildings can get very hot very quickly once they fill up with people and if you're near to a door the temperature changes and drafts can be very hard on your critters
At the show you can put covers over your rabbits and/or keep them away from aisles so spectators don't poke their fingers in cages or offer a bite of a carrot that has been nibbled on by everybunny in the building :groooan:
Doing a quick inspection of other competitors rabbits and notifying the Stewart of obviously sick ones and/or leave the show if you feel your animals are at risk
You really have no control over bacteria and viruses on the table and judges hands but after coming off the table a wipe down of your rabbits body, ears and feet with a disinfectant solution can help remove and kill possible pathogens and lower the chance of them ingesting an infectious dose while grooming