"What is this rounded square multilayer hard plastic part with 65 holes and grooved corners for potentially fitting another piece? Discarded in the thousands alongside a Union Pacific railroad."
A: "Pandrol ‘Anti-Abrasion Tie pads’ — this is what these components are. These are to reduce abrasion of the junction of steel railroad rails and concrete railroad ties."
Meese Inc. was a supplier of canvas bacpacks to US military.
Maybe a US Air Force mail satchel?