How build a toy car that moves without electricity?

I have to make a toy car that moves by itself without electricity. I thought about magnets or compressed air but I don't know :(

The car has to move (go and come back) for 10 minutes on a wood board and I'm not allowed to change or modify the board.

thanksHow build a toy car that moves without electricity?
Just use an old fashioned alarm clock as an engine, it wont drive fast but will last the time, and as I gather it - speed wasn't a subject. Could be alittle tricky to fix a gear to use the whole stored energy in about ten mins, get help from some crafty guy, he will also have the "engine" somewhere in his dusty storage.
School project - like toy cars are more commonly evaluated by distance, not time. Ten minutes also seems an extraordinarily high criteria for a non-battery powered toy car. You will need to conserve the small amount of rubber band, drop weight or spring energy available on that small scale so just arrange the drive for very low speed. Multiple reversals on that undescribed board will be tricky. In that regard, is there a stipulation for minimum distance to go and come back ? If not, then you might arrange for just a rocking back and forth motion. Also, is straight line travel required ? Would a circular path be also acceptable as leaving a position and returning to it ?

EDIT - I really like the adapted clock motor idea from Thorsten. A circular crank arm from the clock pulling a capstan-type drive on the power axle , coupled with a return tension spring could be arranged for the reversing drive feature.How build a toy car that moves without electricity?
Use rubber band power. I used to play rubber band powered airplane,boat or car when I was a kid in China. They ware made of light wood and paper.
look up sterling enginesHow build a toy car that moves without electricity?
how big is this wood board? could a simple steam engine do it or maybe (it can be built small using gears to be propeled)