This was a bit of an onerous task but I took 30 minutes out to record each and every card that I had in my wallet onto my contact manager system (in this case outlook).
It seems that I'm often somewhere where I need my Costco number (to upload and print photos), my library card (to go on-line and reserve a book), or one of my many travel cards. Now it is synced between my computer and my blackberry. Let's see if this helps me or not over the next few months.
Of course bear in mind that if you lose your electronic device all your numbers are going to be listed in full view. I have encrypted my numbers (you could substitute a number for a letter as long as you use the same one all the time; you could change one word into a foreign language, you could put all your numbers in backwards, you could scramble them in some other fashion - just remember to be consistent).