Add a side vent to make a rocket propelled air car. Place magnets on two CD airpucks with all of the magnetic north poles facing up. Push the pucks gently toward each other. So What There are commercial air bearings which can be used to allow one person to push heavy equipment across a smooth floor, Etc. This activity evolved from an older activity using records.
Black vinyl disks with spiral grooves cut in both sides.
Optional construction You can replace the water bottle cap and film can lid with a 2-Liter bottle cap.