Answer:
Used left or right, I get to travel over cobblestone or gravel. Used up, I vie for sweet success, used down, I cause men great duress.
Always old, sometimes new. Never sad, sometimes blue. Never empty, sometimes full. Never pushes, always pulls.
A box without hinges, lock or key, yet golden treasure lies within.
A little house full of meat, no door to go in and eat.
A leathery snake, with a stinging bite. I'll stay coiled up, unless I must fight.
In birth I spring forth, in life I unfold. In death I wilt and die, but rebirth restores all.