I'm not quite 100% cash, but I only keep $100 in the bank and I make a deposit before dropping the bills off at the post office.
I used to think that people who stuffed money in their mattress or buried it in the yard were nuts, but I kept coming across stories like that - the DEA has a whole passel of bank-related regulations for its convenience, long predating 9/11 - and a friend of mine, an active-duty E7, got audited three years in a row. Each time, his first knowledge of it was when checks started bouncing, because the IRS froze his checking account. Didn't help his formerly-perfect credit rating much.
The rest of the world seems to have gone nuts for debit cards. I don't have one. Last month I paid the insurance on the van, $176.36. Handed over two hundreds. Had to wait for the agent to send someone to the back to get change. They said nobody had paid cash there for years. Which wasn't actually true, since I always pay in cash, but before they hadn't had to make change with such a huge sum as $34.67... who could expect them to keep that much money on hand?