At the end of or during most DLCs, you will likely run into unique items that will have high value. At the end of Honest Hearts, there will be a box with unique items, such as weapons and armor. Selling all of it will likely net you this achievement. In Dead Money, in the Sierra Madre vault, there will be several gold bars. If you try to sneak out of the Vault, which will lead you to not having to fight anything, you can drop everything you have and carry the gold bars, which will certainly earn you the achievement.