Clipboard Case Pannier Hooks
Found this clipboard document case at Staples and turned it into a compact clamshell pannier.
Find the printable STL files for the green hooks as well as a few more photos and details at Thingiverse. Alternatively, fork or view the parametric model at Onshape.
Bonus image: sketching a stronger clasp, using a scanned paper trace of the original as an admittedly not very useful reference:
