I mostly stay away from making really specific bike-packing gear like panniers, or randonneur bags, or saddlebags. There is a lot of specific design and construction that goes into them. They inevitably become very expensive, and only good for a very specific use on a very specific bike.
Instead, I make this TRIP BAG. It's a big general-purpose front rack bag. It will fit in a Wald 139 basket. It has numerous attachment points on the bottom and back. It will attach to most front-racks, or handlebars (probably with some added support). You might even be able to run it as a saddlebag with a bag support. You can probably attach a stiff dowel or rod to it if you need the support. Use Voile straps, or webbing, or zip ties. There is a velcro pocket on the bottom to add a stiff bottom.
And it has a detachable shoulder strap and is pretty decent as a sling bag. If you are travelling with your bike, you can use this bag as your carry-on or as your day-day bag without having to attach/remove it from your bike constantly.
Basically this bag is for you if you have a DIY spirit. It won't work for everyone, but it will work for most people who want to hack some day to attach it to their bike.
- 1000D Coruda or X-Pac outer
- Nylon or X-Pac floating liner
- Two 3D front pockets
- Roll top closure with side buckles to compress down the bag
- Extra cargo strap to close an overloaded bag and/or attach addtional cargo
- Velcro stiffenr pocket on the bottom
- Three rows of webbing loops along the bottom and back
- Reinforced webbing loop along back for handlebar or other attachment points
- Removeable shoulder strap