Did you ever park your car in a huge lot, then wonder where it is later? There's a simple solution if you have an iPhone.
Next time your at Pilgrimage Festival or Bonnaroo, here's what you do. When you get out of the car, tell Siri "Siri, remember where I parked my car." It'll drop a pin on Apple Maps.
Then when it's night and you're confused trying to find your car among billions, say "Hey Siri, where's my car?". It'll bring up Apple Maps and look for the pin. It'll guide you straight to your car.