I think the iWatch will also have TouchID and will have NFC.
This way you don't even have to take your phone out of your pocket to make a payment, and with the TouchID, it's so called "secure."
They could make it so the watch knows when you have undid the clip on it so that way when you first put it on you put in the pass once and never need to do it again untill you undo the watch since obviously it's still you. You just made the user experince 20X better and saved money on componets that would also wast space.