Which item is not required to be on service vehicles that transport pesticides?

The correct response is based on understanding the requirements for service vehicles that transport pesticides. A backflow preventer, while crucial in certain contexts to prevent contamination of water supply systems, is not a mandated item on service vehicles transporting pesticides.

In contrast, possessing a pesticide label file is essential as it ensures that operators have immediate access to product information and safety guidelines, which are crucial for safe pesticide application. Emergency medical information is also a required item to provide essential first aid instructions or other medical guidance in the event of an accident involving pesticides. The inclusion of extra shoes can be advised for safety but is not a regulatory requirement.

Therefore, the specification of a backflow preventer as not required aligns with the focus on direct safety and procedural compliance for pesticide transportation and handling.