We used to carry small flashlight when I went out trick or treating as a kid, but we didn't alway use them. Add costume accessories that will light up is a wonderful way to help the child see and be seen.
Lights should be added around thing dangerous. No one wants a kids walking through their garden. The child doesn't want to trip on the garden either. Lights around the garden will keep everyone happy and safe. The lights can be normal lights or the can be any fun or spooky color you would like.
Reflective tape is a wonderful item that can be used in many many ways. When the light from a car shine on it the light will bounce back to the driver so they will see the child/tape. Use the tape on Halloween bags, costumes, shoes, backs, strollers, wagaons, bikes, and anything else you can think of. Reflective tape is also good for decorations as well.
As stated before, if you can walk with the children don't drive. Less cars moving around the less chance someone will get hit. I love the idea of parking the cars and having a location with little or no cars to trick or treat.