Following what others have put in their trucks, I have built a 4' x 4' box for the back of the Suburban. I could have gone with a bigger storage setup, but I have to use the back seats sometimes. The box has 2 drawers and a large area with a hinged lid. I have since added a removable extension (with a headboard) on one side for a mattress for the nights I sleep there. The box holds most of what I carry including: plugs, stove, waders, rain gear, shovel, first aid kit, tow rope, etc. The family refers to Dad's giant tackle box in the back of his truck.
In this pic you can see the crosspiece that I added to support my weight when using the bed, as well as the plug storage in the boxes, rain gear, and stove.
The extension with headboard and mattress are behind the box.
Not in the pictures is the 4' peg board on the left side that holds bags of assorted rigs, bucktails, metal, and small tools. This thing stays in the truck year round. I do a lot of tailgating for football and baseball, so I keep some of that stuff handy in here, too. Good luck with your project.