Background
I'm still working toward my goal of being able to leave my phone in a locker while I work out. Despite the gains of WatchOS 5, it appears that my only real option for music without my phone being nearby is Apple Music (the service) or moving audio files to the watch manually with Apple Music (the app). I'd prefer not to have Apple Music installed on my phone. Googling reveals a lot of articles from the Series 3 release saying that this should be possible now, but I've not found any actual solutions.
Actual Question
Can I listen to music from my Apple Watch without having my phone nearby and without requiring Apple Music be installed on my phone?