ROK straps.
https://www.amazon.com/gp/aw/d/B00SX...?ie=UTF8&psc=1
Bungee cords, for me, have a glaring shortcoming and thats the inability to adjust the size. I am not going to carry multiple sizes.
Rok straps are part bungee elastic and part nylon strap. If you have a lot on the back one day then less the next, they adjust easily and securely.