I walk my dogs. A Lot. Nature calls whenever it wants, but I don't want to have to carry a full bag. I used to, as any good dog owner does, then I saw an advertisement for The Fifth Paw.
An ingenious little device that slips onto your leash. It has two sides and can slip onto thick or thin leashes up to 1 inch wide.
It has three 'hooks' around the outside that will hold poo bags - sometimes two at a time, if you are walking multiple dogs. Just tie a knot, slip it in and away you go.
Learn more and see a demonstration at their website.