Depending on how rugged the roads are and how fast you intend to drive, I recommend tie-down straps for the heavier items like your cooler, water container, and battery pack (if you have one). Trust me that seeing your Yeti cooler hovering at eye level after hitting an unexpected bump on a high-speed desert road is a terrifying experience.
It looks like you have a family, so this might not work for you, but removing the bottoms of the second row seats is very easy and frees up a lot of useful storage space. I usually travel solo or with just one other person, so leave them out most of the time.