A little while ago I asked about how to hang a backpack from a rear rack. The key suggestion by prathmann was to put the backpack's straps on its front, so they don't interfere with the wheel.
And that worked really well! Here is how I'm attaching this beauty to that beauty:
A carabiner attaches the backpack's top handle to the other side of the rack, and a bungee also goes from that side...
... through the daisychain on the front of the backpack, and down to wherever you can hook it. The backpack's dangly straps are tied through another of the daisychain's slots.
And just so you can witness my hamfisted leather-sewing skills, this is how I modified a pencil case to be my tool bag:
I'm learning that you can't have too many carabiners, or too many bungees.