1. Get an empty backpack and put another empty backpack in it.
2. Kill an enemy with backpack and open its inventory.
3. Put one empty backpack from inside of your backpack to ground (right-click on its icon in contents space) => you have empty backpack now. OK.
4. Rightclick on deadman's backpack to replace your backpack with this one. => You now have enemy's backpack, AND enemy still has this backpack! In fact, they work as references like uniforms in Issue 24001. Items shared between all "references" of this backpack.
5. Get deadman's backpack as many times as your patience allows, it will still be there.
6. Put some items in copied backpack => items appeared in all instances, all "references" of backpack. They all share same items. If some unit takes such backpack and removes item from it, all instances of backpack lose that item. (kind of teleporting).
7. If in campaign, returning car loaded with such backpacks with items from scouting mission, on loading camp armory receives full copies (real objects) of all backpacks and all items, multiplied by amount of "copied" backpacks by player. Combined with Issue 23999 can produce virtually unlimited amount of ammunition.