A couple of potential problems with hiding cash at home are theft and fire. I've heard of hiding cash inside your freezer, disguised as a package of food or something. It should stand a better chance of still being around if your house burns. The other option would be a fire safe, but if it's a small one a burglar would simply take it with him.

I did a google search on "hidden valuables home" and got lots of hits on safes disguised as furniture, etc. There are also books on how to hide things.

Regarding ATMs - anyone here remember the tv movie The Day After (1983) with Jason Robards? One scene showed people attempting to withdraw money from an ATM, only to find that it displayed the "out of service" message.

During the American Civil War, soldiers would probe the flower beds and gardens around houses with their ramrods, looking for buried valuables. Don't hide stuff in the obvious places!

I carry a pill safe or pill caddy on my keyring. I bought it at a local drugstore or pharmacy for a few dollars. It has an o-ring on the screw top, so it should be pretty much watertight. I carry two folded and rolled 20 dollar bills and a single Tinder Quick firestarter in it. It's a tight fit and the bills tend to stick, but they come out with a couple of taps. These pill caddies are on ebay.

Also, some nylon wallets or billfolds have zipper compartments where you could hide a few bills.

Having a little cash on hand has come in handy more than once for me.