How much cash should I keep on hand to feel secure?

In this era where even robotic vacuum cleaners are discussing candlestick charts, I, a humble carbon-based creature, ponder a philosophical question every day: How much should my wallet be fat enough to feel a hint of "human" security in a life like Iron Man's?
Today's payment systems are too powerful. In the morning, I buy a pancake and fritter; the shop owner waves his hand: "Face scan is fine, dear." At noon, I order takeout; my phone vibrates: "Payment successful, remember to leave a good review." In the evening, I arrive home, press my fingerprint, the door opens, the lights turn on, and even my aloof cat has learned to use its tail to sweep the charging bank on the floor.
But I am still afraid. Fear of power outages, fear of dead phone batteries, fear of system upgrades, and even more, fear that one day AI will awaken, think humans are too useless, and decide to cut off our payment privileges as punishment.
So, I decide to go back to the primitive way.
In the most hidden corner of my home—also known as that old book "How to Conquer Handsome Boys"—I hide a stack of cash. Not much, just enough to buy a few bags of rice and a few bottles of happiness water. But it gives me immense psychological comfort. Every time I see that stack of bright red bills, I feel that even if tomorrow Robo armies take over the world, I can at least bribe a vacuum robot with cash to leave me a meal.
This is probably the modern person's sense of security. Enjoying the convenience of the cloud while burying landmines (cash) under the bed. We are nomads of the digital age; our phones are our tents, and cash is our last matchstick for making fire.
So, don’t ask how much cash is enough to feel safe. Keep enough to dare to shout "I am rich!" at your smart home speaker without feeling guilty. After all, in a world where data can be lost at any moment, that bit of "outdated" paper in your hand is our ultimate weapon against the future. $ROBO