This lets you pay for Starbucks using your watch. You can also view your balance and rewards information.

(This is based on the 2.0.1 version of the PebbleBucks app by Alexsander Akers. His 3.0 version is currently not working for a large group of users, so I'm putting this modified/fixed version of 2.0.1 up for people to use in the interim.)