Answer:
I help you carry your books.
I can fly but I have no wings. I can cry but I have no eyes. Wherever I go darkness follows me.
I come in different colors and shapes. Some parts of me are curvy some are straight. You can put me anywhere you like but there is only one right place for me.
In the sun I like to play; in the rain I goes away; walk or run I always follow; in the mud I always wallow.
What did the thief get for stealing the calendar?
I go in hard, come out soft. Blow me hard and I'll make a pop. What am I?