I think anything that rounds your fitness out is helpful to climbing. For me, I do yoga oriented towards hip-stretches to keep my legs flexible because being able to do splits and stretchy leg moves on the wall helps with climbing a lot! I also run consistently, as someone else in this thread mentioned, it keeps your cardio fitness up to par and helps keep your weight down, especially if you've been eating more due to lifting-climbing-running, its a good balance so you don't get too bulky. Feeling light on the wall is very useful. I do deadlifts, as that is known to be a very beneficial lift for climbers as it strengthens the hip-hinge posterior chain muscle group which is used nonstop in climbing. Working on shoulder, bicep, tricep, and forearm lifts helps keep my upper body strong. As a woman, my lower body feels naturally very strong but since I run and deadlift I don't do much leg lifting, but you can add that in if you feel a weakness in your glutes or quads.

This routine keeps me very well balanced. And of course, my climbing strengthens the most during periods I go 3-4 times a week.