Which of the following is essential for deer hunters to carry while hunting?

Carrying a hunting license is essential for deer hunters because it serves as legal proof that the hunter has completed the necessary training and has permission to hunt in a specific area during designated hunting seasons. A hunting license ensures that individuals are abiding by state regulations regarding hunting, which helps conserve wildlife populations and maintain safe hunting practices.

The other options, such as a dog leash, fishing pole, and food supply, are not mandatory for deer hunting. While a dog leash may be useful if a dog is involved in the hunt, it is not a legal requirement for deer hunting. A fishing pole is irrelevant to hunting, as it pertains to a different activity altogether. Although food supplies may be necessary for longer hunting trips, they are not legally required for the act of hunting itself. Thus, possessing a valid hunting license is crucial for compliance with wildlife laws and ensuring responsible hunting practices.