Pay with Apple Pay
You don't need to even grab your iPhone to make a payment. If you can use Apple Pay at a location you can make the payment with your Apple Watch. Apple Pay is a mobile wallet that is currently on the iPhone SE, iPhone 6, iPhone 6 Plus, iPhone 6s and iPhone 6s Plus and the latest iPhone 7 and iPhone 7 Plus.
Add Apple Pay to your Apple Watch using the Apple Watch app on your iPhone and then double press the button below the crown to pull up the Apple Pay option in stores and then touch your watch to the reader.