Which task is NOT required to be completed prior to passenger boarding?

The task of ensuring all seats are occupied is not required to be completed prior to passenger boarding because the actual occupation of seats happens during the boarding process itself. Passengers will find their assigned seats as they board the aircraft, and it is normal for seats to remain unoccupied until they physically get onboard.

In comparison, checking potable water levels, chilling white wine and beers, and ensuring cabin cleanliness are all essential tasks to be completed beforehand. Checking the potable water levels is crucial to ensure that there is enough clean water available for passengers and crew during the flight. Chilling beverages, particularly those served cold, improves the overall onboard experience for passengers. Cabin cleanliness is vital as well, as it directly impacts passenger comfort and satisfaction during the flight. Therefore, these activities are prioritized before boarding, while ensuring all seats are occupied can only be assessed during or after boarding.