First you will have to make flash cards on cars. I found a car picture on Microsoft Word and used it. Write out the contraction on each card; for example write out "he is" or "they will".
Let each student read the two words on the flash card. After they read it, have them drive the car flash card and crash it into something. It is more fun to have them make the sounds too! When they crash the car, bend it in the middle so it becomes the contraction. The apostrophe is the crow bar to pull the word apart again. Then, have them read the contraction.
Just a tip - you might want to bend the words ahead of time so you can do it quickly when you are with the kids.