When I did finance work/interning at a casino in college, there was this idea that the required amount of cash to keep on hand was http://www.casinosformoney.com/how-much-money-does-a-casino-keep-on-hand:
Every single slot machine hitting a jackpot at the same time,
Every single chip that the casino had on hand, and
Every single outstanding payment to players.
It was generally close to $100 to $120 million. Higher on the weekends, lowest on Tuesdays and Wednesdays.
As part of my initial "tour", I got to see the cash room. I had to change into a pocketless one-piece jumpsuit (which is what the cash handlers in the back room and cash wranglers at the front of the house wore at all times, while handcuffed to their steel cash cart).
The first room was exactly how you'd expect. Minimalist, extremely bright, buzzing lights. Like something out of Men in Black. There were cameras trained on all points and a guard positioned at a door that looked just like a bank vault.
The finance VP took me through that door and into the actual cash room.
Jesus fuck.
It was amazing. Stacks and stacks of hundred dollar bills situated behind bulletproof glass boxes strapped and locked down to steel and lead shelving systems bolted to the walls, towering twenty-five feet into the air. Heavy rolling ladders like you've seen in libraries were situated one on each of the sides of the room. Three men in the middle of the room counting cash using http://www.cumminsallison.com/static/loaded_images/ticket,-currency-counting,-check-scanning-solutions-CumminsAllison-3551.jpeg and talking shit about football (American football, mind you), occasionally writing down figures on a clipboard before re-checking.
One wall was empty except for four large doors. I asked about that, and my explanation was as follows (paraphrasing, it's been several years):
"Our bank's armored cars back up into the area where the door is, and is suctioned and locked into the door frame like an airplane is attached to a terminal for passengers to pass through."
I asked how much cash was in the room that day, and how much had gone in and out since the day began. She walked over to a computer station on one end of the massive table in the center of the room and logged in and tapped some keys.
"$14.8 million coin-out, $110.2 million cash reserves."
I was in a room with $110 million in cash.