The weighted chin up is an excellent exercise for developing vertical pulling strength, grip strength, and core stability. If you don't have access to a weight belt, you can place a dumb bell between the thighs, just above the back of the knees (then bend the knees during the exercise to stabilize the weight).
You may notice I placed the plates behind my legs. This is a technique I discovered that decreases wavering of the plates during repitions, so that strength can be focused on instead of excessive stability. The plates behind the legs technique places the added weight more directly under your center of mass, so that you don't have to fight to stabilize each rep.