A couple of years ago I read a book entitled 'You're Broke Because You Want To Be' by personal finance author and reality TV show host Larry Winget. In this book, he briefly mentions how he carries around a $100 bill in his wallet. He stated that this action gives a person confidence, knowing that emergency cash is readily available.
Since then, I've stashed a Benjamin in my wallet. On a couple of occasions, I've used it instead of my debit card. For example, on one occasion, my wife and kids and I were visiting relatives in Las Vegas. The oil pressure light came on the day after we arrived. I took the car to a repair shop, and they performed an inspection. Everything checked out OK, except for the oil pressure sensor. Confident that we could return home safely without replacing the sensor, I only needed to pay for the inspection, which was around $80. So far, we had kept to our cash only travel budget.
Because this was an unexpected expense, I pulled out my trusted cash and paid the shop. I was happy because I had a small emergency stash available when I needed it. When I returned home, I snatched a $100 bill from our automobile budget envelope.
Carrying cash allows me to have confidence that while standing in a checkout line, if my debit card doesn't work, I can pull out cash and avoid an embarrassing situation. It also gives me one more reason not to carry a credit card for so called 'emergencies'.