What term refers to smaller items that help fill available space in a bag?

The term that accurately refers to smaller items used to help fill available space in a bag is "fillers." Filler items serve the essential role of occupying gaps that may exist after larger items have been placed in a bag or container. This ensures that the bag is efficiently packed, preventing contents from shifting during transport and protecting fragile items from damage.

In many scenarios, fillers can also facilitate the optimization of space within a bag, allowing the overall load to be more stable and manageable. This practice is particularly useful in retail and shipping environments, where maximizing bag or container space contributes to overall efficiency.

Other terms in the choices, such as sidewalls, loose items, and crushables, do not specifically capture the concept of items meant to occupy gaps in packing. Thus, "fillers" is the most relevant and precise term in this context.