Things like this are why I love Apple's self-checkout system at its stores. No need to even go to a checkout; just scan the item with your phone, and it's paid for.

I sometimes feel like a shoplifter on my way out, but nobody's ever looked at me sideways.

More than once I've decided to pick up an adapter or headphones or a hard drive at the Apple Store instead of Fry's or Best Buy or Target because of the iPhone checkout.