Here's some additional information to add to our body of knowledge about caching cash. This evening on Dateline the episode was "
The Betrayal of Sarah Stern". It examined the disappearance of a 19 year old girl. During the episode it was revealed that Sarah was going to leave town and live on her own after discovering a little more than $25k in cash that had been squirreled away for her by her mother. The mother died of cancer in 2013. Shortly before Sarah Stern disappeared, she was going through family belongings in an old house and found a safe, which contained the cash, which she put in a safety deposit box at her bank. During the police investigation they found the cash, which was described as deteriorated and in poor condition. Some of the bills crumbled when handled. Since Sarah was born in about 1997, and her mom died in 2013 we can say that the cash is in the 15-19 year old range. The Stern's lived on the Jersey shore. If we consider the environment we would realize that it is near salt water in an area that sees the full turn of all four seasons. And even though this money was kept dry and in a safe, it still deteriorated significantly over a period of less than 20 years, and possibly far less since we don't know when her mother began putting this money aside for her. This money would have been handled by many people over the years before ending up in that safe, picking up trace amounts of various chemicals, acids, alkalies, bacteria and other substances. So I think at this point we can say that even in relatively dry conditions, cash is subject to a lot of deterioration, at least to the point where it would be hard to use in transactions, probably including trading it out at a bank without having to provide some kind of explanation.
EDIT: At a later point in the program, during the trial, testimony was that the money was found by Sarah Stern in a shoe box. I don't think this is too significant since it was most likely kept as dry as it would have been in a safe. And by the way, spoiler alert: The people involved with Sarah Stern's death were two of her best friends, one of which she knew since she was a small child and the other dude took her to prom. The alleged motive was that the guy who did the killing was after the cash and had planned the killing for months.