I personally almost never carry cash any more, the only time I really use cash is when out drinking or going to a really tiny corner shop/off licence where they still charge extra to pay by card. I use an oyster card for my public transport (or my debit card if I'm out of credit), and pay for most my small purchases using contact less, I can pay for parking by phone, and I still have a debit and credit card for anything bigger.
Why would I pay for any high value goods in cash, when I can put it on my credit card, get chargeback protection and still not pay any interest on it?
You are proud of being dependent on the system? If there is a a power outage or if the debit system goes down, good luck getting anything without cash.
I recall being at a movie theatre lining up to purchase tickets for a popular title when the debit system went down in the area. Fortunately, I had cash so I was able to get into the theatre and see the film while all of the "winners" with only debit and credit cards got to go home.
Do not bother calling yourself an adult if you do not carry around enough cash in case of an emergency or just simply to pay for really small purchases.