Final answer:
For setting up a channeled rigid video laryngoscope, a Bougie should always be readily available to aid with endotracheal tube placement during difficult intubations.
Step-by-step explanation:
When setting up a channeled rigid video laryngoscope, the adjunct or device that should always be readily available is C) Bougie. A bougie is a flexible device used to guide the endotracheal tube into the trachea, particularly when the view of the glottis is poor or the angle makes intubation challenging. While other devices like a Miller blade, stylet, and LMA (laryngeal mask airway) can be useful in airway management, the specific question focuses on the preparatory setup for a channeled rigid video laryngoscope, where the use of a bougie can greatly assist with tube placement.