After rolling the tonneau cover back or crawling on my belly to retrieve items that skidded to the front enough times I went with one. I use it more to the inside than I have used it to the outside. Mine is the AMP Research extender. They make a couple different styles, but I don't remember what the one I have is called.
I pulled it off my old truck and added it to my new truck. It didn't add resale and after having it I can't imagine being without it. Even when I load up the back end for trips I keep it in there and work around it. In the picture the front 2 totes are winter weight and the back tote I keep in there to hold items from rolling around.