Which of the following is essential for an officer to carry at all times while off duty?

Identification credentials are essential for an officer to carry at all times while off duty because they serve as proof of their identity and authority. In situations where an off-duty officer may need to identify themselves, such as witnessing a crime or being approached by a member of the public seeking assistance, these credentials validate their status as a law enforcement officer.

Carrying identification helps establish credibility and can be crucial in scenarios that require immediate law enforcement intervention. While the other choices—badge, extra ammunition, and flashlight—may be useful in various situations, identification credentials specifically provide the confirmation of an officer's duties and responsibilities, making them vital in maintaining public safety and trust even when the officer is not in uniform.