WMIK (Weapons Mount Installation Kit) British military Defenders
Lots of interesting stuff is part of the WMIK setup.
In official British military parlance they call this tailgate a Pannier. They're used as a place to store gear; I've seen ammo cans in them and other items. A tailgate (er... pannier) like this one could be implemented for a Jeep, although you'd need to find a different place for the spare (on the bonnet?). The spare on a WMIK Defender is located on the side of the roll cage, it can be seen in some of these photos.
The one above is a faux WMIK, someone has installed surplus WMIK bits to convert their civvie Defender into a WMIK clone (note no weapon installed on top, and the Defender decal on the back). This next one is a real WMIK:
The Land Rovers pictured above also has lockers installed in the sides. You can see these on some of the photos above, it's the hatch right behind the doors. It's an easy installation in a Land Rover but I can't find any place in a Jeep where something like this, even if smaller, could fit.