Advance Healthcare Directive
This is a legal document that lets your physicians, family, and friends know your health care preferences in the event that something was to happen to you.  In this document, you would name an agent (usually a spouse or close relative) to handle your health care choices for you.  You could also list your preferences as to prolonging your life by artificial means, if you prefer to be buried or cremated, if you prefer to donate your organs for research, etc.