Are you creating a mugging database?
Around town, I usually have an average of $100 on me. Whenever I get down to around $50, I hit the ATM for $200 and draw that down.
If I go on a road trip, I usually have $200-$300 on me, with lots of small bills. Part of that is for stuff like paying for breakfast, so I don't have to wait for the server to bring the credit card back in a busy restaurant, or picking up a bottle of water or a snack when I gas up, etc. Also, I have found, due to what happened to me on a road trip last year - my credit card number getting hijacked in the middle of the trip - it's good for a fallback, or paying for gas at a sketchy gas station.
Additionally, I keep a few Jacksons hidden in the vehicle for when I inevitably go to the grocery store and forget my wallet.
Sometimes it feels like I have to work to use cash instead of a card. Every time I do so at Costco, I have to get the cashier's attention because they're so accustomed to people using cards.