I'm 38 years old and have been going to shows since I was a teenager (my dad had a show quality '33 Chrysler Imperial Coupe in stock condition). What I've learned from shows is this, the car has to be impeccable. That means a show quality paint job without streaks, swirls, etc...etc...etc... If it's got a horrible paint job, people will walk right by it without even stopping. Also, the interior should be spotless, even going so far as to remove the floor mats. A brand new looking carpet with a clean heal pad is much better to look at than floor mats with wear spots. There should not be anything other than the necessities in the interior (I've seen people with garters hanging from their rearview mirrors, clothes in the backseat, portable CD players with ugly wires laying on the seats, etc....etc...etc.... Under the hood, uniqueness and cleanliness goes a long way. Oh yeah, make sure each door window is down and that the rest of the glass is clean, with no streaks. That's about it as far as detailing goes. Cleaning the car is something that may take you 2 to 4 hours, depending upon what you need to do. Sometimes before a show, I may have to remove some trim and repaint it Black. Of course, this slows down the process! I clean the car the night before and when I arrive at the show, I only have to do a light wiping.
As for what to bring? Well, you need to bring all of your cleaning supplies and cloths, folding chairs, sunglasses, suntan lotion, cooler full of ice water and maybe a small umbrella that mounts to your chair. It certainly gets hot, especially in late June, July and into August.
Don't get caught up with winnning a trophy. No matter how nice your car is, there's somebody out there that has one that's nicer. Also, the trophy is only a $10.00 item anyway. Why get upset if you lose?
I usually vote for cars that are unique. If you've got 10 cars that basically look the same, it's hard to pick a winner. I look at EVERYTHING, including bolt heads, trim, straightness of the body, shine of the paint, overall appearance, etc...etc...etc...
My car has been to 8 shows since 2004 and I've won the "Editor's Choice" award for MM&FF magazine, a Best of Show for all Mustangs between 1974-1993, four first places, one 2nd place, and one 3rd place. I was able to do this without the aid of a Supercharger or a Turbocharger. I used a dual quad setup and detailed the hell out of the entire car. In the engine compartment, I glass beaded and primed/painted everything, including all bolts that hold the fenders and hood on. The only polishing that I do, is to my valve covers and air cleaner lid.
My advice is to make your car stand out, without the aid of every tacky gizmo that you can buy. Tasteful mods and changes will definitely be in your favor. Good luck!
Oh yeah, one more thing. Once you start accumulating trophies, don't bring them to the shows and show them with the car. While I've never done it (too much of a hassle anyway), I've heard judges mention many times that they're not fans of displaying the "bling".