Porteur bags are large capacity front bags based on the bikes and racks of French newspaper deliverymen from the mid-century.
Porteur bags are great when you just know you want lots of room to carry stuff. I prefer a larger bag in the cold months when I'm likely to be carrying multiple layers of clothes, more food, and other just-in-case extras.
-two rear 3-D pockets,
-one large front 3-D pocket
-bottom leather wear patch
-hidden side D-rings for shoulder strap
-elastic lid closures
-waxed fabric: $20
-RaClip rack attachment clips $30
-4 bottom velcro attachment straps $20
-shoulder strap $12
-interior pencil pocket $25
-1/16" ABS plastic stiffener sized to fit $15
-coroplast stiffener sized to fit $10
-brass and leather buckle lid closures $20 each
-dynamo wire port $10
-size modifications $20
-Dock-It™ ready (interior flap and landing patch $25
One customer's requirement was for a bag that could carry a dozen eggs and a six-pack. The distinction between a porteur, a demi-porteur and a large handlebar bag is a difference that's hard to quantify; once a bag goes beyond 10" wide and 6" front-to-back it's probably in the demi-porteur zone, and once the bag reaches 8" front-to-back its reached full porteur status. For a bag of this size you'll want to have a porteur rack in place to support both the contents and the footprint of the bag. You can find racks available from Velo Orange, Soma, or a custom maker.
Please note: despite the name, "handlebar" this type bag generally requires a rack for support and often a decaleur for stabilization--this is even more true for porteur bags.