Store temporarily only accept cash due to some error? Replace panic with nonexistent queue.
Regardless of whether you always pay cash or always pay with a card and regardless of whether you value privacy or not - you should always, in my opnion, have some cash with you. That has served me well and I've never in my life regretted having too much cash on me. The day I get robbed the cash I have on me is the least of my worries, if anything having an empty wallet might be provoking to someone that just tried to rob you (or a lot of money might get him (or her) greedy and ask for more, you never know).
Note to self: Get rid of (and remember) the CCV code on the card and destroy the magnet stripe on my card. Anything not working with the chip isn't worth the hassle nor worth the trust of using a card (that might sound strange for some but in Sweden the use of the magnet stripe is quite rare).