What is typically found in an "overhead bin"?

The overhead bin is primarily designed for passenger luggage, and this is the most accurate response to the question. Passengers are allowed to store their bags, coats, and personal items in these compartments during the flight. This setup not only keeps the cabin organized but also ensures that the aisles remain clear and safe for movement.

While emergency equipment, cockpit instruments, and flight crew supplies are crucial for flight operations, they are not stored in the overhead bins. Emergency equipment is typically located in designated areas easily accessible to the flight crew, while cockpit instruments are housed within the cockpit itself. Flight crew supplies are usually stowed in specific storage areas designated for crew needs, separate from passenger storage areas. Therefore, the designation of the overhead bin as a storage space for passenger luggage makes it the best choice for this question.