Here is some useful information about what you should have when driving in Spain. read more here.
If you wish to see as much as possible of Spain then having your own car is certainly the best method of transport, even if it may take you a couple of days to feel confident about driving on the opposite side of the road. As an EU citizen and a tourist, to drive a foreign registered vehicle in Spain you must have with you, and you can be fined for not obeying the following:
1. your passport, current until after your return home
2. Current driving licence, preferably the EU type with the ring of stars
3. Two EU approved, red warning triangles
4. Approved reflective jackets that must be worn by all outside the car at anytime, day or night, outside the vehicle at the side of any highway not in an urban (street lights?) area. The jackets must be kept inside the car so they can be put on before getting out and also must be visible from outside the car. The pocket in the back of the front seat is a good place. The jackets are inexpensive and can be bought at most supermarkets if you do not have them already
5. A set of spare lamps/bulbs for your car and the tool/s to change them
6. If you wear corrective glasses for driving, a spare pair
7. Your number plate should be an EU one with the ring of stars containing your country code, or a small plate/sticker with your country code (GB, etc) should secured to the rear of the car
8. Valid insurance
9. All vehicle documents relating to the car (legally certified copies are OK)
Recommended, but not mandatory is a First Aid kit and a fire extinguisher
It used to be that you had to carry a set of bulbs with you but this has now changed. The law has realised that with most new vehicles, changing a bulb is impossible anyway as they are sealed units. Therefore it would be unreasonable to insist on carrying spare bulbs.