What if I lose my car keys?

Have you ever thought what happens if one day you go market and after coming back you notice your keys are gone?
Let me give you a real example: Once on a early morning I parked my car in a parking lot and I was walking up to my workplace that I noticed a car key on ground. I searched around but could not find any track of the guy who had lost his/her key. Then, I took it to the parking manager and tried to make sure they will take care of it till his owner come and I take it.
When I reached my office, I thought what would happen if the same scenario happens to me? What happens if this time I lose my keys when I go hiking in nature.
To get rid of these worries the idea came to me was that: I simply print my phone number on a piece of paper then stick it my car key in order to be called by finders (of course if I will be enough lucky that somebody finds it before it gets too late).

Please, leave your commends if you have better idea. ^_^