Instructable-maker Greg Clarke came up with a great way to make DIY bicycle panniers from backpacks that allows you to maintain the backpack's functionality... meaning you can remove the pannier and then strap it onto your back, and no one's the wiser.
- webbing, or fabric that you really trust. Webbing is everywhere, though. You could even trim a little off of a strap off your bag. I pulled mine off of a suitcase i found in the trash
- bungee cord that isn't too long.
- bicycle with rack
- needle and high quality thread or floss
So, no sewing machine required. Awesome.
Read the full instructions: Backpack Panniers (That Are Still Backpacks)