I use these: Light & Motion GoPro Mount and Light & Motion Urban 350

Don't ride much in the dark these days, but that's the set up I used when I did. Would've preferred a Cygolite as I was very happy with their headlights, but only Light & Motion offered a GoPro mount at the time. Glad to see Cygolite has one now too.

Garmin Varia and a Cygolite HotRod for the rear lights.