This is a slight diversion, more like DIY bag customization. I like to have a small bag for packing extra layers into or for carrying my picnic lunch on charming days. I also keep finding "handlebar bags" that seem the right size but I don't like the dangling design with two straps around the handle bar, next to the stem, that leave the bag hanging and bouncing against the control cables. I've had some success with taking that basic bag and changing the attachment methods to suit my purposes. I'll move straps, lengthen straps, change ladder lock straps to hook and loop, fabricate stiffeners, add tie downs, etc,,,,, as needed. Works for me.
^^^ is a Canondale bag with a nice size and shape. I fabricated a simple "rack from electric fence wire and a bit of cherry hardwood. I then made a wooden stiffener for the back of the bag, replaced the original straps and attached them wider to clear the center of the handlebar and added a tie down to wrap around the HT, stabilizing the bag under load. Good enough for a sandwich, carrots and some chips.
^^^^ Sunlite barrel bag that, again, was a useful day trip size but would not play well with the cables on the front of my Y2K Cannondale. I'd made the wooden package rack years ago and found that, by removing the original straps, making and then turning a new one and adding a bit of hook n loop to the bottom it mounts on that rack well and is stable. Room for a tool roll and picnic lunch.
^^^ another simple barrel bag what would never suit me lashed to a handlebar. This one needed an internal stiffener which I made out an empty (and washed) kitty litter jug. I then removed the original straps and fabricated quite long hook n loop straps that are fastened on one side and long enough to wrap around the bottom (and the luggage rack its sitting on) and up the other side to close across the top. This one sits along the rack like a trunk bag, either on the rear of one bike or the front rack of another. Good for a day trip or even as a bit-o-extra when I have the panniers on the front rack. Suitable for purpose