I would get a hard case for the camera, then place it in the back pack. Pelican has some great cases if you're shooting with an SLR. Otherwise, pad up your back pack.
depending on if it is a large camera, or a digital, you could put it in a sack that goes on the back of your seat (because it never hits the ground) or a backpack. Camera's are never really safe. Taking it biking is risking it anyway. A backpack or the seat pack are probobly the safest options period.