The Guaranteed Rotating Extra Board (GREB) position at BNSF involves being on call to cover vacancies when permanently assigned employees are absent. This role includes various responsibilities such as janitorial duties, driving crew vans, operating equipment, and managing inventory. Safety compliance is paramount, and employees must adhere to company and federal safety regulations. The position requires flexibility in working hours, including nights, weekends, and holidays, and offers guaranteed 40 hours of work per week.