I carry a canon 40D (quite on old camera nowadays!) along with a standard zoom (17-50), a spare battery and cleaning cloth. I occasionally also carry a mini telescopic tripod and gopro. I use a dakine snowboarding backpack, its a heli-pro (20l I believe) something like the below. Of course as you know the more gear you carry the heavier it is, especially noticeable on the hills! I doubt your gonna find a bag that can protect camera equipment from a impact fall (unless its some kind of hard-case, in which case it will probably injure you!) I think you perhaps need to take less risks and ride at like 80% – safe in the knowledge that your equipment will be in one piece at the end of the ride!
https://www.dakine.com/en-gb/bags/backpacks/snow-backpacks/heli-pro-20-liter-backpack/