Answer:
I work when I play and play when I work. What am I?
I am a cave full of bones and the house of a worm.
Sometimes I am white, sometimes I am dark. Most people love me. What am I?
The faster you run the harder it is to catch me
I am a little piece of paper, yet sometimes hold lots of value. I am all you need to get into big events, but will cost you. I am an important part of travel. And if lost, you're not coming. What am I?
Brings the sky a lot closer.