For that I just use my phone. It's way more awkward to pay with the wrist anyway the way the terminals are set up. I do agree it would have been nice to have MST on the watch, BUT unless you're really into leaving your phone behind (and paying the exorbitant amount of almost-double-the-price for the LTE version...it's listed as 450 for the base LTE model at BestBuy), does it really matter VS the heavily improved sensors and digital bezel?
PS: For those asking, yes, the promo codes do not work for pre-orders (so no free wireless battery pack unless you pre-order outright). Not sure if the free battery will apply only for pre-orders or if it will still include it when it's released a the end of the month (once it's on sale, the code CAN be applied, as they stated above).