This folding, pedal-free electric bike designed by VW, made its debut at Auto China 2010 and is designed to fold up and fit in your spare tyre comparment. The Bik.e is capable of 12.5 miles on a full charge with a top speed of 12.5 mph, and it's designed to draw a charge from the car itself so you won't need to worry about plugging it in.
The idea is not particularly to use the bike for emergency breakdowns; it's more for helping you reach a destination that the car alone cannot access, or where parking is not available where you want to go. Apparently this is not just a concept - the bikes will be marketed, although pricing information has not been released. A video at the link shows the bike in use.