While downloading music to the device seems pretty straightforward, I'm disappointed to see that only a handful of my iTunes library is eligible to go on to the watch. Since most of what is eligible are the older songs I used to pay for individually (before I subscribed to apple's streaming service) I figured I could just go in and purchase a few on my jogging playlist outright. However, in iTunes there is no such option for these songs (it only says "play").
I know this is more of an iTunes issue than a 645M one, but I'm disappointed and seem to be stuck. I figured Apple would love another way to take my money, but it doesn't seem to be the case here.