Boat operators should have which of the following on board?

The correct answer is C. Nautical charts and related documents.

Explanation: Boat operators should always have nautical charts and related documents on board to navigate safely and understand the waters they are operating in. These resources provide essential information about water depths, hazards, and navigation aids, which are crucial for safe boating. While other documents may be important, having up-to-date charts is vital for safe navigation.