When I was younger for our old dog we always used grocery bags/kitchen disposal bags for poop bags. Buying them and paying extra for something like that was unfathomable to my parents. Alot of folks carry on in this way and don't ever buy poo bags. I can understand not wanting to pay extra for picking up your dog's excrement. Now I buy them because they're eco friendly, convenient, easy to use, and often nicely scented which helps for the duration of time it has to be with me before it lands in a trash can. They aren't that expensive either - usually below $9 for something like 120 bags. On occasions when I've been truly skimped and money couldn't be spared for bags (I used the money for treats, food etc instead) I switched over to bio degradable plastic grocery bags.