Which of the following documents must be in the car while driving?

The requirement for having specific documents while driving primarily revolves around ensuring that both the driver and the vehicle are legally compliant. One of the key documents mandated to be carried at all times while operating a vehicle is the driving licence, which serves as proof of the driver's qualifications to drive. Additionally, the car registration document is essential because it verifies that the vehicle is officially registered and roadworthy, and it also provides necessary information about the vehicle.

In contrast, while an identity card may be useful for identification purposes, it is not specifically required to be carried while driving. A parking disc is only relevant for parking regulations and does not pertain to the legal operation of a vehicle on the road. The technical backup certificate and spare wheel, although potentially useful in a breakdown situation, are not mandatory documents that one needs to carry for legal driving purposes. Lastly, while having a spare tire can be practical for emergencies, it is not among the required documents for legal driving. Thus, the combination of the driving licence and car registration is essential, making the correct answer clear.