Wrap the cabbage, corn, carrots, and bamboo shoots in a clean cheesecloth or tea towel and squeeze to wring out excess moisture. In a medium bowl, use your hands to combine the bok choy, celery, mushrooms, broccoli, sesame oil, salt, and pepper, and mix until well blended. Gently fold in the cabbage, corn, carrots, and bamboo shoots, and mix until fully incorporated.