Be prepared for loss or theft!
A friend recently lost his wallet. Another lost his keys. Both had no easy reference to what was lost, and had to spend days tracking and replacing what was lost.
My suggestion? I always have a set of duplicate keys on a keychain in my dresser drawer. Car, house, mail box, and in my case, storage room. When I get a new key I make sure I get two, or I immediately have one made. So if I lose them I instantly have another set, which I would immediately have duplicated again.
I also keep a photocopy of both sides of my credit cards, drivers license, passport and other documents that I keep in my wallet. If lost or stolen, I can quickly stop the cards, and start the replacement process for the other documents.
When traveling I keep a copy of my main passport page in my luggage. If my passport is somehow lost, it greatly facilitates obtaining a replacement from an embassy or consulate. I keep pictures of all my documents in the cloud, too.