How should I stay fit when my broken clavicle is healing?

Healing fracture. Exercise by walking and avoid movement in the shoulder area. Live a healthy life style. Eat a balanced diet with lots of fruits and vegetables. Take a multivitamin made from food, and multi-minerals with calcium, magnesium and zinc. Do not smoke.
Walk,ride. If it is not painful, you might try walking, or riding a reclining cycle at the gym. Nothing too strenuous which would jar the clavicle. You must rest it for some time before trying anything. (i had same thing, i understand) just be careful. Good luck.
Have a Look! Here are two links that may be helpful for you! http://www2.Massgeneral.Org/sports/protocols/clavicle_fracture_protocol_after_surgical_repair.Pdf http://www.Livestrong.Com/article/491556-post-clavicle-fracture-exercises/.