I don't think of myself as that old (in my 40's), but I am amazed when I go out with people in their 20's - and they literally have less than $5.00 in their pocket. It's not like they don't have money or a job - they just don't carry cash.
I like cash - it's a universal language. I keep an emergency supply, in smallish bills, hidden in my house for unexpected events (blackout, emergency repair, forgetting to get cash the day before the cleaning woman comes over, etc.). I also typically withdraw an amount of cash that I think I will need for the week once a week. It's simple, and there are often times when cash lets me cut the line ("next customer paying cash only," screams a cashier whose machines have broken down).
The #1 reason for carrying cash -- discounts. In any country in the world. You can literally go anywhere and, if you tell the salesperson that you're paying cash, you can bargain down the price of anything. We've done it on furniture, appliances, clothing, antiques - really, anything. We were furnishing a family home abroad and went to a particular store for some furniture. By the end of the transaction, we were given a 450 Euro chair for free, as well as discounts on the other items we purchased - all because we were paying in cash.
So yeah, I get that the credit card is convenient. I also love using those self check-out lines at CVS - and I charge it even if it's only a couple of bucks. But it won't kill you to have some cash on you, no matter where you go.