I would bring the 18-55mm. Car shows means tons of people, and you may have to get really close to the cars to make sure no one can get between you and the car. That means you'll need to go as wide as possible.
Honestly, I would be pretty good to go with just that. I don't know what you would need a telephoto for, unless there was some sort of presentation or show on a stage and you wanted to take pictures of the action. Maybe bring the 55-300 just in case?
Bringing along the 50mm f2 might not be a bad idea as it's small anyways and you can use it for people shots.
Those are my suggestions.