The best practice is to set them to:

  00000000

Just in case you need to use them, you know.

https://web.archive.org/web/20120511191600/http://www.cdi.or...

Implanted in a volunteer's chest cavity:

https://en.wikipedia.org/wiki/Roger_Fisher_(academic)#Preven...

Use a bicycle lock: http://news.bbc.co.uk/2/hi/7097101.stm

You keep them on a plain .txt file, of course.

I think they keep them in a briefcase.