Below are links to the websites where you can purchase these same items. Most of them are affiliate links so I will get a small commission each time you purchase something through my link :)
GoPro Hero 5 Black Edition
I do like the Hero 5, although the audio isn't as good, but I think the video quality is the best for POV cams out there.
GO PRO HERO 4 BLACK EDITION
The GoPro Hero 4 is a very trusty camera, reliable since it came out in 2014, Since the Hero 5 didn't introduce any new res/frame rates or bit rate increases, the footage from the Hero 4 is still very good!
I love my GH4, great quality camera, 4K 30fps is awesome! Small form factor, it's great.
Zhiyun Rider-M Gimbal
I am quite happy with this gimbal, I am getting great stabilized footage with this!
Sennheiser MKE 2 Elements
This is probably the best audio setup I can think of for mountain biking. It only works with the GoPro Hero 4.
GO PRO CHESTY
The classic chest harness, a must have for any gopro user.
ZOOM H4N DIGITAL RECORDER
I really like the audio quality I get from this recorder, I use this with my GH4, connected with a line in cord, and it goes straight to the cameras audio track.