> it's incredibly convenient to have each time it's required

Sadly there is an increasing preponderance on the part of retailers to do one of two things:

    1. Go card only (sadly happening in far too many places)
    2. Make it incredibly difficult to pay by cash (e.g. 10 card tills, 1 cash till with long queues because it is also the cigarette/lottery ticket/package collection till)

The only people remaining who will almost kiss you for offering cash instead of card are taxi drivers.