Answer:
Man's most important invention.
Some keep it in a dumpster while others keep it in their trunk.
It goes up and down the stairs without moving.
What word becomes shorter when you add two letters to it?
No matter how little or how much you use me, you change me every month. What am I?
Two little holes in the side of a hill. Just as you come to the cherry-red mill.
Easy
Animal
Difficult
Food
Funny
Kids
Logic
What am I?