Everyone should carry a window breaking tool in the car. It's basically a sharp pointed metal rod on a spring. You release the spring, the point contacts the glass with speed and force, and the impact breaks the window.
Here's one of many of these tools, this one's only $10:
http://www.chiefsupply.com/resqme.phtml
Those will make great Christmas gifts for my girl friends. We do a gift exchange every year with a $10 limit. We all have children and this will be perfect. Thanks for the link!