Answer:
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?
Poor people have it. Rich people need it. If you eat it you die. What is it?
I am useless when together but useful when I am broken apart. What am I?
In a tunnel of darkness lies a beast of iron. I can only attack when pulled back. What am I?
I'm written with two letters, said with one and seen with two. What am I?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.