Keys - house, office and car - are tiny tools we use everyday. Loosing or breaking one slows you down and is often expensive. Make yourself spares (multiples!) now, and you can thank me later.
Keep a spare with your dear wife, wallet, in a desk drawer, man purse, clipped to your jacket or with a neighbor.
The voice of recent experience?

The big one is to make sure you buy the third key from the auto dealer when buying a car. If you lose one encoded key, it costs a small fortune to get a replacement made because you need to have 2 encoded keys at all times.