I sometimes carry a large ammo can or a cooler on a rack that hangs over my spare tire...
It's worked out very well, so I've been thinking about a similar mounting method for a dedicated ammo can carrier. It would hang over the spare, and carry two 50-cal/FAT 50 ammo cans, one on each side of the spare. A ratchet strap would run around under the tire to secure the rack in place, and make it easy to remove when necessary. The can holder would be adjustable so it would fit multiple tire sizes.
I've done some photo editing to create a few concept images...
A rack like this might not be on the Jeep at all times - because it's easy to install/remove perhaps you'd really only need to install this rack when you were making a trip where you needed to carry stuff in the cans. For example, recovery gear isn't usually needed in everyday driving, so maybe the gear would go in the cans and only be carried on off-road trips.
In addition to a can on each side of the spare, it would be possible to build the rack so that it could hold another can or two, or perhaps a fuel can or Rotopax container.
I haven't built one of these yet, so far I've just been playing with the photo edits above to figure out if this is a dumb idea or a useful one... ?