Hotel Key Cards
Granted, this won’t work everywhere, but you can keep your hotel key cards on your iPhone. So long as you keep your iPhone with you, you won’t ever have to worry about your key card.
You can add the key card to your Wallet before or after check-in. If you do it before, the hotel will activate it as soon as you check in online, and in many cases you can head straight to your room without stopping at the front desk first.