What should be used when an aircraft does not have branded products for the partner you are on?

The correct choice is the GSK, which stands for Generic Supplies Kit. This kit is essential because it contains unbranded, versatile supplies that can be utilized when a specific partner's branded products are unavailable on the aircraft. The GSK ensures that crews can still provide a standard level of service and meet basic passenger needs, even when familiar branding is absent.

By having access to the Generic Supplies Kit, flight attendants can maintain operational efficiency and uphold service quality. This kit typically includes a range of items that can be used across different airlines and partnerships, allowing flexibility in service delivery and ensuring passengers are taken care of even in less-than-ideal inventory situations.

In contrast, the other options focus on specific supplies or contexts that do not adequately address the need for a substitute for branded products. The LAV Supplies and Flight Attendant Supply Box relate more to specific onboard functions or personal use rather than a general substitute for partner branding.