I would suspect a failing fuel pump relay or the pickup for the immobiliser slipping.
Always carry a relay, the modern ones seem to fail with monotonous regularity.
The immobiliser pickup slipping is not common, but several have suffered (with others losing the chip from the car's ignition key). Worth checking whether your spare key will start the car. However, as you manged to start the engine after several attempts at the supermarket I suspect a slipping pickup is more likely.
