Answer:
I can be as thin as a picture frame but my insides have many things you can see.
You can tumble in it, Roll in it, Burn it, Animals eat it, Used to cover floors, Still used beyond stall doors. Freshens whatever it is placed on, Absorbs whatever is poured into it. What is it?
What has a ring but no fingers?
What always comes into the house through the keyhole?
What is found over your head but under your hat?
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.