You will have more than one job; more than one career during your lifetime.  You must invent and reinvent yourself over and over.  The New York Times is addressing this (a bit) by showcase five individuals.  Need more cash?  What can you do?

http://www.nytimes.com/2013/01/13/business/how-5-older-workers-saw-a-chance-to-remake-their-careers.html?src=me&ref=general