This is what you need to carry in your car whether you own a car here in Spain or just hiring one (you need to check).
Proof of Identification, Insurance and Ownership document or Car Hire document
Spanish vehicle 4 wheels or more need to carry two warning triangles (Forgeigh registered cars only need 1)
If you wear glasses to drive you are required to carry a spare pair at all times.
High visibility jacket – this should carried in the car at all times and must be warn at a breakdown or exit from your vehicle.
All British registered cars must display a GB sticker if their number plate does not have the EU one.
If you own a right hand drive car you must have the lights converted.
Like most places it is illegal to talk and drive unless you have a hands free kit. Radar detectors are banned although you can still use your GPS systems.