Let's say you've been gone for 10 days. When you parked at the airport parking lot, you stashed your car keys in a pocket or in your carry on bag. After all, you won't need them for 10 days.
Now you're riding the shuttle to your car...and you can't find your keys.
Plan ahead and find the keys before you get on the shuttle to the parking lot. If you've really lost them, you can deal with it at the airport terminal instead of standing in the dark by your car taking everything out of your bag.