Secure Tite Mini Cargo Net 15" x 30"
Item #: 317632 | Model #: 61444
Got it a Lowes for about $10
This one fits like a glove for the back of my 2door. It is the size of the thing you lift to get to the tire jack. You can stretch it to the rear seat attachment hoop( I have the seat removed) to the gate. So it roughly covers half of the rear. The 2012's have a bunch of tie down places to attach the hooks. It looks like maybe older JK's don't, but I would think the 2011's would. The holes are about the size of a large grape fruit. You might want to try to find something 30" X 30" with smaller holes to cover the whole back area. Just do a search for "cargo net" plus the size you want.
I would also recommend getting some larger bungee cords to keep with you for big bulky items.