What should I do after towing a car with a shopping cart in it, being late for 'Isha prayer, and not waiting for or looking for its owner, who is most likely not Muslim?

If your hitting of the car was by mistake, there is no sin upon you, for the Messenger of Allah, may Allah’s prayers and peace be upon him, said: “Indeed, Allah has forgiven for my Ummah (nation) their mistakes, their forgetfulness, and what they are forced to do.” However, you erred by not asking about the car owner to compensate for what you damaged. If you predominantly believe you can find him, then search for him. Otherwise, estimate the damage and give its value in charity to the poor or for general Muslim welfare, knowing that the property of a Muslim and a non-Muslim are equal in terms of guarantee.