Answer as to what to put back there: anything and everything! That's the kewl thing about Receivers. Whatever your Mind can come up with/see on the Road, you can do from the square Receiver format. I flipped a drop down Hitch of mine upside-down. I rested a scrap of Particle Board laying around to the Hitch while it rested level between the Hitch and the rear Bumper top. I bunge'ed down an instant, el cheapo Table for 1 on this stable 3 point mount [left and right side to Bumper; 3rd support point on Hitch]. Handy to cook on sans a 'real' Table that trip of Boondocking super-light...
With Battery Power run to something like a 7 Pin Bargman Connector, you have +12 VDC back there for Light down on whatever you mount, or for any reasonable amperage load. I can't find them this second, but there's a whole series of Adapters that are Bargman -> ...fill in the blank... One neat one converts to a Cig Lighter Plug for whatever.
Hold up a quick-disconnect, '3/4-round' Shower Tent bent out of Conduit attached to square Hitch 'stock' Metal once set-up in Camp?
We've got a 'swing-away and lock open' Yakima 4 Bike Holder. Just the very stout, lower swing-away part could be a Modular Table mount or whatever you fancy. There's 'anti-rattle' Pins for Receivers that minimize lateral slop for tight Receiver mounting of 'whatever'.
My Brain works along the lines to make mounts and things 'modular'. To repeat Rob above a bit, you can adapt functions on the fly as you notice neat Accessories while Camping or at the Truck Stop. In good Weather, support that Flat Screen in the shade to watch The Big Playoff Game!
