Which preparation is essential for high-risk stops?

The preparation that is essential for high-risk stops is securing loose items in the vehicle. This practice is crucial because loose items can become projectiles during sudden stops or maneuvers, potentially causing injury to the officer or passengers. Securing these items helps ensure that all personnel remain safe during the stop, allowing the officer to focus on the situation at hand without distraction.

In addition, having a clear, organized environment inside the vehicle can improve response times and maintain control during high-stress situations. This preparation supports the officer's ability to act effectively and maintain safety, which is paramount during high-risk encounters.

As for the other options, while recording license plates, increasing speed during approach, and using an unmarked vehicle can each have their advantages in specific contexts, they do not directly address the immediate safety concerns that securing loose items does.