Minimise the inconvenience
Replacing car keys is not cheap. Normally the cost is around $70, but it can be up to $3,000 in some cases and if you have an imported vehicle you might have to wait several days or more if authorisation is required from overseas for the dealer to issue new keys.
For newer makes and models, the car key is often part of the vehicle's security system. If you lose the key you may have to get the system re-coded.
If the key is damaged, and needs to be replaced, you should be able to get a replacement key from your local dealer. If you lose the key, but it's unlikely to be used by anyone else - for example, you drop it over the side of your boat while fishing and you still have the master key, you should be able to get a replacement from your dealer.
You generally get two master keys with a vehicle, the master key operates everything in your vehicle, and is programmed for your car, so replacing it can be inconvenient and time consuming. If you lose your master key and you don't have a spare, you may need to replace the body control module or at least have it reprogrammed.
If your keys are stolen and it is possible that the thief could come back and steal your vehicle, you will need to reprogram or even replace your vehicle's body control module for peace of mind.