Which protective container is often associated with shipping goods without caskets involved?

The correct choice is the combination case, which is specifically designed for the shipping of goods while providing a protective encasement that does not involve the use of a separate casket. Combination cases typically serve as both an outer shipping container and an inner burial container, usually made of strong materials to ensure the contents are well-protected during transportation.

This design is particularly advantageous as it reduces the need for multiple containers, streamlining the shipping process and potentially lowering costs. Additionally, combination cases can be used for a variety of goods, making them versatile in logistics and shipping.

In contrast, other options like the metal case, casket liner, and air tray serve different purposes or are not designed specifically for this kind of shipping protection. Metal cases often refer to strong, durable shipping containers used for various items, which may not be as versatile for all types of goods as a combination case. A casket liner is typically used within a casket for additional protection and cushioning of the deceased and is not meant for general shipping. Air trays are lightweight containers generally used for shipping fragile items, but do not provide the same protection and structure as a combination case for heavier or more delicate cargo.