I don't do any other exercise than riding!
Although I do ride my bike in a way to also keep my glute and core muscles engaged all the time to keep them strong. The gluteals are used a lot in walking, running, and climbing (on foot). I also frequently do near-sprint-effort intervals at high resistance to stress my bones enough to help prevent bone density loss.
For a few reasons, I need to maintain decent running climbing performance but without having to do any exercises other than cycling. I simply don't have time to do both and alternating days for running or cycling doesn't really work for me.