What essential safety item should a diver have in case of a lost fin while diving?

Having an extra pair of fins is essential for a diver in case they lose one while underwater. Fins are crucial for propulsion and maneuverability, and losing one can significantly hinder a diver's ability to swim effectively. With an extra pair of fins, a diver can quickly replace the lost fin and continue their dive safely, maintaining control over their movement and ensuring they can return to the dive site, exit the water, or maintain safety during the dive.

While backup equipment like a diving mask or a snorkel can enhance safety, they do not directly address the issue of lost fins. A compass, though valuable for navigation, does not help with mobility. Therefore, having an extra pair of fins stands out as the most practical safety item for this scenario, allowing for immediate assistance in maintaining the diver's mobility and safety in the water.