Car shows are tough... The cars are really close together, there are people everywhere, it's tough to get good shots.
- If it's indoor, take a tripod and a flash. Show cars aren't going anywhere, you can afford to use slower shutter speeds.
- If it's outdoor, take a CPL to get rid of reflections. Shoot early in the morning or later in the afternoon, shooting at high noon makes for very harsh lighting. Plus, getting there super early is better since there won't be as many people there yet. Taking a flash for outdoor shooting is also good for fill flash, since the cars aren't always in the perfect position relative to the sun.
- Be mindful of your backdrop. If you can manage it, avoid having things like trees or light poles directly behind the car so that it appears that they are "growing" out of the car.
That's off the top of my head, I'll revisit this when I get back from work. Have fun with the show!