You could try things that don't put too much pressure on the ankle or knee. Right away my thoughts jumped to chin ups and pull ups! Or try push ups with the one foot off the ground, this can be done on the knees as well with one leg off the ground. I would mainly stick to upper body work until the ankle is healed. I would avoid doing pistol squats with the good leg because the other one will be so weak in comparison that when you get out of your cast you'll have a huge imbalance.