Answer:
So cold damp and dark I am. To stay you would refrain yet those who occupy me do never complain.
I am one small little piece of paper yet sometimes hold lots of value. I am all you need to get in to big events but will cost you. I am an important part of travel. And if lost you're not coming.
Part carbon part water I am poison to the fishes. Many falsely claim my name I am the pause that refreshes.
I go up when the rain comes down
I belong to you but others use me more often than you do. What am I?
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?