If you’re hauling a collection of individual objects, especially heavy things like wooden boards, you don’t want them to be loose and flapping all over the place. If you’ve got a pack of slats in your truck bed, every bounce and jostle on the road will send them knocking against each other. Not only is this kind of annoying, but if they keep bouncing off of each other, they could loosen their bindings or damage each other, not to mention scuff your bed liner.
If you’ve got a bunch of objects in the bed, try to group them up together, then pack them up tight. Bundling a bunch of loose boards into a single, sturdy rectangle will keep them steady and prevent them from jostling each other or the truck. You can do this with some stretch wrap from the hardware store, supplemented by ratchet tie-downs. If the objects you’re hauling don’t easily fit together, use stretch wrap and a cargo net to wrap them all up into a cohesive whole. It doesn’t have to look pretty — you’re going to take it apart when you get to your destination.