Basically the walking stick. The fool completes a journey through the tarot deck and hence is usually represented with a walking stick, on a horse, with a pack, or on the top of a mountain...
The mountain represents that he is about to step off of the cliff into manifestation.
Normally the fool card has all four elements in it (earth = mountain, water = frozen snow on mountain, air = more air on top of mountain, fire = normally there is a sun...).
He is called the fool because he begins his journey knowing nothing, but comes out at the end knowing all there is to know about life and death.
Its actually really hard to explain the fool without going into an exlination of all the other cards in the Major Arcana... if you really wanna know you can always write me a note and I would be happy to enlighten you