Image by Cthomasuscg via FlickrCars movie theme, you'll need:
White spray paint
4 Orange cones (can be found at the dollar store)
Boxes (banker's box size, but make sure the handles are on the longest sides of the box) Cut out the bottom
Black Paper Plates (regular size)
White paper plates (small)
Cars movie theme stickers
Additional colored paint (optional for painting the boxes prior to the party)
If you are going to paint you boxes different colors, you'll need to do that first, then you'll need to attach the Velcro to the back of the plates and to the boxes. Make sure that you attach the correct sides to the boxes since you'll be attaching the white plates to the "front" of the box to serve as headlights, and the black plates will be attached to the sides to serve as the wheels. You will need to spread the 4 orange cones out far enough to allow 2-3 adults to stand (they will serve as the pit crew), and use the spray paint to create 2-3 lanes in your "track".
As your guests arrive, give them 4 "wheels", 2 "headlights", stickers, and ask them to assemble their cars while they are waiting for the remaining guests to arrive. The kids will like the activity, and they will use the assembled car in a race later at the party. Not all of the kids will want to race, but they should enjoy the activity.
Once your pit crew is in place, you can start your races. Each kid will need to step into their box, and hold it up with the handles. They will each run one lap around your track. There will be some crashes and some stumbles since it is a little difficult to run carrying the box. Your pit crew will need to get the car (kid) off of the track immediately and re-assemble the car should they want to continue to race. Upon completion of the lap, you'll need to wave the checkered flag to indicate that the race is over. Each child can get a trophy if you opted to use trophies, if not they can keep their car as a party favor.