Answer:
Sing me to a baby about to go to sleep.
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?
What bone has a sense of humor?
Tool of thief, toy of queen. Always used to be unseen. Sign of joy, sign of sorrow. Giving all likeness borrowed.
The more you work the more I'll eat.You keep me full I'll keep you neat.
No matter how little or how much you use me, you change me every month.