You'll need the
Tombstone Park, which will, upon death, spawn a tombstone that you’ll be able to retrieve in your next game that will contain all of your backpack's inventory.
This park can be gained as:
- a lootable soda can available as a contract reward (possible to exfil)
- rewarded as a random perk power-up when someone completes their story mission
- bought from a perk machine on map
- a blueprint
If earned as a drop from a contract reward, you can stow it, exfil, and save it for later to bring it on a run specifically for this achievement.
Once it's activated, die, don't be revived, and quit. The next time you spawn in a DMZ instance, you'll find a tombstone icon on the map. It will be in the same location you died previously. You could spawn near it, or across the map.
Navigate to it and loot your tombstone to unlock this. You will be able to loot back the contents of your backpack, but will lose things like the armor, gas mask, self revive, and rucksack. It may be worth trying this after a failed exfil where you don't have good gear, or on a 2nd character from your main.