I've put many cars (and motorcycles) into a bazillion car shows over the years, some casual shows, some Nationals shows, and some Concourse De Elegance shows; some with 25 cars, and some with 3000 cars (Mopar, Chevy, Ford, Jaguar, Lotus, Ferrari, Maserati, MG, Yenko, Saleen, AMC, Crosley, Indian, Chopper, Shelby, Etc). In some shows I had up to nine vehicles in one show. I've also helped organize some shows. So it's alot of fun to do, if you enjoy that sort of thing.
*** Alot of good advice was given here. Personally, I wouldn't bring an EZ up canopy, no matter what the fastening method. I've seen one fly as high as 50 feet in the air on a windy day. Everyone was standing there screaming as it flew over the show cars and came crashing down on two beautiful Corvettes. I then saw the owner of the canopy zooming 50 miles per hour out of the parking lot, without his car..
***Also, as stated previously, don't touch any cars and don't let anyone touch your car. It's kind of an unspoken car show etiquette, but alot of unknowing people still do it. Once I walked up to my car at a show and saw two butt cheek prints on the hood. I was fuming until I noticed that my girlfriend unexpectedly showed up and was wearing a mini-skirt.
***Yes, yes, yes, let kids sit in your car. It will stay with them as a great memory for years (it did for me when i was a kid). Don't be afraid to let enthusiastic show goers, (and select nice women) sit in it too.
***If your car is lined up with alot of the same type of car, you will make friends fast. The other owners will want to know how you did this and that.
***Ask people questions about any car that piques your interest. Car show owners love to talk about their cars and could talk to you for an hour about it if you had the time to sit around and listen.
***As stated previously, make a plaque (nothing fancy, 8 /2 x 11" on white paper if nothing else is available) with a short explanation (about a paragraph) about your car. People like cozying up with a good read about an interesting car. Make the text jumbo, so people can see it from a distance and then walk to it to read the specifics. I usually tape mine to the windshield.
***Don't disappear from your car for too long. Go out an explore the other cars, but check back and hang out with your car every now and then, to talk with interested parties. There are always those cars at shows that are parked like they're in a mall parking lot and the owner is M.I.A.
***Roll down your windows so people can see inside. It really bugs me when people put their car in a show with all the windows up (especially dark tinted windows). Your car is at a "show", so show it to people.
***Clean the inside of your car. You'll notice that some people leave a pile of dirty laundry, empty soda cans, and a baby seat in the back. It just doesn't make sense.
***COME AT THE START TIME AND LEAVE AT THE END TIME. There's nothing more annoying than spotlighters that show up an hour late, stay for a couple hours, and then leave. At car shows where spectators are paying $$ to see the cars, they are paying for a product: to see the cars. So if the show is from 9am to 3pm and you have to sneak out early to get to work at 1pm, then don't go to the show. Spotlighters leaving early also have to disrupt the crowds as they creep in their car towards the exit. They also leave gaping holes in the car lines where they were parked.
***Get your significant other involved. Nothing makes the day sweeter than your other half supporting you in your hobby. My girlfriend was gracious enough to sit with me for hours in the hot sun, in show after show; but I thought she might enjoy it more if she had more participation. So I let her drive the cars into the show (everyone typically stops and watches as the cars roll into a show, she liked that). Also, instead of her sitting on the sidelines all day, I bought her her own Mopar (Chrysler's TC, for all you enthusiasts of lesser known cars) and she would prep it and put it into the shows with me and my cars. She had so much fun talking to spectators about her unique car that it was hard to get her to leave the shows! Then after you both get home, be sure to go with her to her six hour craft show.
***If it starts to rain lightly, don't have a meltdown. Your car has been wet in the past, and the drizzle usually blows over after a few minutes. But do sit back and enjoy the frenzy of the garage queens whisking their cars away into their 50 foot air-conditioned trailers.
***Leave the time-out doll at home.
***Have fun.