Should cyclists carry ID? Yes, and why I do
New South Wales planned introduction of compulsory rider ID is causing controversy:
Government to bring NSW riders to heel - Bicycle Network
The fine and compulsion is not good but I think all cyclists should carry ID. I take this as —should something go wrong — along with ID one word might help someone else: Donor

UPDATE 03/8/2016: Mark Hanna has a great post on what the word Donor on your licence actually means and more information on becoming a donor:
Are You an Organ Donor? - honestuniverse.com