Avis distributes its rental car keys in duplicate. There is a plastic Avis tag, a hard wire keyring, and there are always two keys attached. Car keys today are massive, usually having the remote for the doors built into the key handle. Having two of them attached to each other inseparably makes for a bulky package to keep in a pocket.

I cannot figure out why they are doing this, and nobody at Avis has been able to tell me. You can’t use two keys at once. They are stuck together. If you lose one key, you lose the other as well. So why is the second one there?

The only thing I can think of: When they sell the car in their fleet program a year later, they still have both keys.

Which would be a very strange reason to bother numerous renters with during the first year. To meet a secondary objective (eventually selling the car with both keys) they annoy their primary customers (the renters) with this very inconvenient situation.