I have been doing car shows for the past 7 years and have some advice for you. Be sure to plan out all the small stuff and get permission from all the businesses envolved, if any, before printing your flyers. A checklist of things to do would include:
1: Location. Find a suitable lot to hold the number of cars you are expecting. Most businesses will let you hold a car show but if they don't own the lot, the management company must give permission and address any liability issues for possible damages during the show.
2: Charity events. Contact the charity you wish to support and discuss with them what you are doing and how any money raised will be donated to them. Be sure if they have any type of logo that you have their permission to use it on your flyers. Logo permission also applies to any businesses that may sponsor the car show that will appear on your flyer.
3: Get sponsors for door prizes, dash plaques, and trophies if possible. These promote the sponsors and cut your overhead costs for the show by reducing out of pocket expenses. Most businesses are more than happy to donate prizes for a charity event. Hit up car parts stores, restaurants, and any other local businesses close to the event site.
4: Source suppliers for your dash plaques and trophies and order them at least a month in advance so they are ready. The internet is a great source for dash plaques if you don't have a local supplier. Trophies are usually best gotten locally due to shipping costs.
5: Flyers should be made and distributed at least one month before the event. Internet car show sites are great for posting the event and may reach people outside of your area. Be sure to include a contact number and name for directions or more information. Some radio station sites also list charitable events for free and may announce them on air as well.
5: Two different colored raffle tickets (door prizes and/or 50/50 drawing), a box or jar for the tickets, safety tape, tables, chairs, signs if needed, a sun shade, pens and markers and anything else you may need for the registration area and to block off the show area.
6: A 50/50 is always a good way to raise extra money in addition to the registration fees. Silent auctions are also good.
7: A DJ is nice and needed for announcements and general entertainment. Be sure they have appropriate music and a system loud enough to cover the event area. 60's and 70's music always works well for a car show. (Sorry Fastback)
8: Registration forms to be displayed on the cars during the shows. Should include a reigstration number, make, model and year, driver name and city if you wish. I find having the driver city on the form can start a good conversation plus gives you a good idea on how far they came from to be at your show.
9: If no restaurant is within walking distance, a mobile food vendor will ususally come out and work just for what they make during the show. Check your yellow pages for a vendor. Also make sure trash cans and restrooms are accessible for the show.
I know I may have left something out but these are the main things you need to plan. Hope it helps.