I should clarify that I carry it everywhere during the week when I'm working. I have needed it many times. Most small towns I work in don't take debit/credit. If I need an oil change, being I drive 1200 miles a week on average. If I blow a tire in the middle of nowhere and need a new one, again small town auto shops usually don't take plastic. I blow 3-4 tires a year, 500 miles a week on gravel is no good on tires. If I'm in one of those small towns and need gas at a station that is cash or check only.
If I'm going out in Des Moines, no I don't carry a checkbook.