Answer:
This is rectangular, hollow and has a lid, and where you’ll find it you might wonder, it is just six feet under. What is it?
You use it between your head and your toes, the more it works the thinner it grows.
If you break me, I do not stop working. If you touch me, I may be snared. If you lose me, nothing will matter.
A mile from end to end, yet as close to as a friend. A precious commodity, freely given. Seen on the dead and on the living. Found on the rich, poor, short and tall, but shared among children most of all.
A precious fluid, thicker than water.
What is yours but only used by others?