What items must be carried by all cabin crew on duty?

The requirement for cabin crew to carry specific items while on duty is rooted in safety and operational protocols. The correct choice highlights items that are essential for maintaining safety and effectively managing emergencies.

Carrying a Flight Manual ensures that cabin crew have access to critical procedures and policies, which is vital during flight operations. The Signed Dangerous Goods document is crucial for identifying any hazardous materials on board, enabling the crew to handle emergencies effectively and comply with regulations. Prepared emergency cards serve as quick reference guides to protocols that must be followed in various emergency scenarios, enhancing the crew's ability to respond promptly.

In contrast, while the other options include important items, they do not encompass the specific protocols necessary for responding to emergencies and ensuring passenger safety in the same comprehensive manner. For example, options like uniforms and ID badges, while necessary for identification and professionalism, do not directly relate to emergency preparedness. Similarly, items such as emergency water and snacks might support passenger comfort but are not fundamental to the immediate safety responsibilities of flight attendants.