My father kept 40 dollars in an envelope taped to the top of the glove box, enough at the time, to get the car towed home, because of inflation I keep 200, but taped inside a panel in the dash. It has saved me more than once. The other car advise my father gave me was to buy your wife a small gift from her favorite store and keep it under the passenger seat, so if there is an anniversary, birthday, etc that you may have forgotten you can just grab the emergency gift.