Take your late-game advanced survivor, with all his skills, knowledge, mutations, bionics, what have you. Drop everything you carry, save game. Go to your world folder, find the .sav file. Generate a new world, with 0.01 item drop rate. Place your .sav file in the new world’s folder.
Essentially your character starts naked in a new world where there’s next to no loot and probably a lot of tough enemies due to time having passed since start of cataclysm. You’re 99% likely to start in a forest unless you increased city size.
For a milder challenge, bring along your equipment (or parts thereof). If you have an RM13 armor and crowbar, you can pretend to be “Gordon Freeman” instead of “Kyle Reese”.