The only thing I can think of is buying and selling large quantities of Bitcoin. That is kind of strange but not unheard of entirely. I used to have an uncle (he died 30 years ago) that lived through bank failures a couple of times. He didn't trust banks. He kept all of his money hidden in a metal box somewhere in the woods behind his house. When he died several of my relatives destroyed the land behind the house looking for the box and never found it. That's a rare case but who hates banks more than Bitcoiners?
Yeah, I understand. But keeping such cash at your own home and not in some pre-arranged location away?
Our ex-CFO had a relative who died approximately in 2000, never had SSN (edit: or maybe he had it but never used it as an adult) nor bank account, did all transactions with suitcases of cash. But collecting his estate was a multi-week trip around the country to visit all the places where he stored it (mostly regular safes/storage as well as some hidden caches on his properties).
Edit: I know that e.g. European illegal immigrants to the USA, especially those who don't speak English well, tend to store/deposit their savings also in cash with the neighborhood groceries/restaurants/bars/bodegas/convenience stores. Sort of like Leon: The Professional
http://www.imdb.com/title/tt0110413/ . But storing at home?