A sabretache was a flat bag that hung next to the light cavalry trooper’s sword.  It was use to carry orders across a battlefield.  Roman legionaries carried a “loculus,” a kind of cross-body haversack.  Today, we carry bags of similar design to carry computers, tablets, books, papers, phones, and any number of things.  I prefer to use hand dyed veg tanned leather, hand stitched, and solid brass hardware.