Which flag is displayed when other flags are not available for general display?

The post flag is specifically designated for use when other flags are not available for general display. It is utilized by military installations and can often be seen in use during regular duty. The post flag is a standard-sized flag that represents the installation and maintains a consistent visual presence when circumstances prevent the use of other flags like the garrison flag or storm flag.

In contrast, the garrison flag is larger and is flown on significant occasions or during holidays, while the storm flag is smaller and designed for adverse weather conditions to ensure that it remains undamaged. The memorial flag is mainly associated with honoring those who have passed and is not regularly displayed. Therefore, the post flag plays an essential role in maintaining visibility and representation at military posts under normal circumstances, making it the correct choice for this particular question.