This taken from the Department General of Traffic (DGT).
There are three documents that you must carry, and they must be valid, whenever you drive, for all types of journeys:
1. Driver’s License.
2. Vehicle Registration Document.
3. Vehicle Technical Inspection Card (ITV).
Carry these 3 documents, either originals or certified copies, whenever you drive, as they will be the first thing requested by an officer if you are stopped or involved in an incident. Remember that since 2008 it is not mandatory to carry the insurance policy or the receipt of the last payment in the car.
These documents are also required for rental vehicles. Before starting to drive a rented vehicle, make sure that it includes the mandatory documentation.
Remember that within the MiDGT mobile application, you have available your driver’s license and the registration document of your vehicle, with the same legal validity as the physical documents to drive within our territory.
CAB adds that of course personal ID. Spaniards DNI. Foreigners passport or ID from country of origin, TIE or green registration certificate.