Klick Fix offers a rack top QR system for bags and baskets
http://www.klickfix.com/index.php?lang=en


reusable Zip ties work for Me, though the single use work fine ..

and if you can open up the pawl with a small screwdriver , they can be reused too ..


I got one of Paul Comp's Flatbed front porteur racks.. it has a rail around it to retain stuff..
and lots of stuff fits .. even a 40cm Pizza Pan.