Messenger bags-A history.

Girl messenger arriving at the Foreign Office with an Admiralty despatch-pict from the Yorkshire Film Archive

Via: messengers.org:

• The single-strap shoulder bag as used by messengers is really nothing new, in the scheme of things. Such a design is almost universally seen through history on the shoulder of almost any type of messenger, whether it be Pony Express, postmen, running messengers in many an early civilization, or bicycle messengers from the era of the telegraph messenger boy to the present.
• The messenger bag as we know it today, however, originated in the 1950s or thereabouts, being produced as a bag for telephone linemen, by Globe Canvas/De Martini in New York. The linemen needed a bag they could easily access while climbing telephone poles, and this design worked perfectly. New York bicycle messenger companies picked them up sometime in the 1970s, and initially were purchased one color per company, as identifiers of a sort. For a long while, NYC was the bastion of the messenger bag - until things started to spread in the 1980s.
• Manhattan Portage lists their start-up date as 1980, and while I've not seen their early bags, the basic design of their modern bags is, like most everyone else's design, directly traceable to the De Martini bags. They claim as their firsts the use of Delrin buckles (rather than metal loops) to close the bag flap, and the use of Cordura (rather than canvas duck) as exterior material. Both claims have also been made by Zo Bags in San Francisco, which started in 1984, directly influenced, again, by De Martini. Zo Bags can, however, securely claim the introduction of one-piece construction (of the outer covering; previously, makers like DeMartini and Manhattan Portage constructed the flap as a separate piece, which necessitated a seam across the top of the bag), as well as the 3-panel bag design (currently used by Timbuk2), and the waist strap. Courierware, in Boston, started up in 1985, but never seemed to gain the same popularity amongst the messenger community as the other early/mid-80s starters.

Eric Zo's web page letter to the world...

• 1989 brought the beginnings of San Francisco-based Timbuk2 (originally called ScumBags) and Toronto-based (now in British Columbia) Pac Designs. These 2 companies were the forefront of the 3rd generation of modern messenger bags, inspired by their own interpretations of the DeMartini design as filtered through the lens of Manhattan Portage, Zo Bags and Courierware. Pac ushered in the blossoming of the highly-customized messenger bag, taking a leap from the very basic "big bag with a shoulder strap" to offering bags that converted from single to dual shoulder strap arrangements, and a whole spectrum of add-ons, pockets and subdividers

Chrome's med sized messenger bag

• The early 90s brought Bailey Works (Portsmouth), Push (Toronto), Chrome (Denver, now SF) and Roach (Vancouver - one of the first, if not the first to introduce a 2-strap backpack-style bag) hot on their heels, initially with mostly local appeal (used to be that if you saw someone with a Bailey, they were almost certainly from Boston or Minneapolis; someone with a Roach was nearly always from BC - the advent of CMWC and the Internet changed that quickly enough...) They were followed by a host of other manufacturers from across North America, Europe, Australia and Japan, all working hard to satisfy the unique demands of bicycle messengers everywhere. regardless of whether they prefer simple single-shoulder bags, super-custom shoulder or convertible bags, or dual-strap backpack-style bags.
• Frank DeMartini passed away in early 2000, but his bags continue to be made to the same pattern they always have been, by a former employee who bought the company shortly before his passing. I often wonder if he knew the lasting influence on a subculture his creation had, some 50 years down the line...