As a poor young guy in around 1980, I made due. I got some kids school back packs. To stiffen the bottom and keep the back out of the spokes, I cut up a milk crate from the grocery store. One crate did both sides. I cut it into an L shape and this also was used to mount to the rear plescher rack of the 73 Super Sport for a solo ride from NW Ohio to Southern Ohio to visit a college buddy. It was a 600 mile circle tour by the time I returned. They held up for the trip. I had a lot of weight on the back but made it okay. I still have that bike, rack, and front bag. I don’t recall what I did with my makeshift panniers.