I usually prefer to use webbing straps with buckles for lashing the major bits of gear to the top of the rack. Webbing can be tightened down to whatever length you need, it doesn't stretch, and it tends to remain in place once adjusted. It also won't suddenly let go and take your eye out like bungies. I do like to use a bungee cargo net over everything else, but not to keep the big stuff down - rather, this just gives a handy place to stash small items like handkerchiefs, bandannas, jackets etc when not in use or drying out.

Neil