If you happen to carry any electrical stuff like hair dryers or just a simple charger for your mobile telephone - you will have to take into account that the electrical systems admit only the 2 pin round plug as shown in the picture. If you are coming in from Britain you might want to buy an adapter to be able to use your stuff in Spain. It may be a little difficult to get it in any normal electrical store. If you happen to have a El Corte Ingles department store near you - they sell adapters for different systems.
The Spanish system is compatible with most European plug sockets – except mainly for the British 3 pin plug - so get that adapter.
Luggage and bags:
Bring an extra one to cart back some of the excellent food and clothing that can be found here. Or buy one at the mercadillo for 15 Euros to take stuff back with you.
Clothing/Shoes/Weather Gear: Sandals - probably better to pay Spanish prices here. Spain is still home to a thriving shoe industry and they're sold at very reasonable prices. The mercadillo has a huge selection for under 10 euros.
Toiletries and Medical Supplies: Forget it. Everything is likely cheaper here than where you're coming from. If you forget something just buy it here.
Camping/Beach/Outdoor Gear: Beach towel. If you forget, you can find them all around on the explanada.
Miscellaneous: Bring a great attitude and a smile, along with some knowledge of the Spanish language, and you'll get along great.
Luggage and bags:
A fold up bag is useful to bring presents back. Either bring one or buy one here.
Clothing/Shoes/Weather Gear: If going out of season consider taking a small umbrella. They are expensive to buy in Spain. Also a waterproof coat.
Photo Equipment: Bring your camera as there are a lot of things that you will want to keep a memory of. Digital cameras are less bulky than the SLR and you won't need film!
Camping/Beach/Outdoor Gear: Either bring a beach towel or purchase one when you arrive; because hotel towels although fantastically clean, can be a little rough.
If you bring your alarm clock radio with you as I do, and it runs off the mains, don't forget to bring your converter plugs with you as Spanish plug sockets are TWO PIN ROUND !
Voltage is the same as in England BUT where as our voltage is closer to 240v AC, Spanish voltage can go as low as 206v AC, especially at peak demand times. Your appliance will work o.k. but say, a kettle will take longer to boil.
Many people bring their mobile phones with them but DO remember that a call from the UK will cost YOU even to receive the call. If you are going for a long period, consider buying a Spanish mobile phone, two if you are going with company. Then you can keep in touch with each other when at different locations and CHEAPLY. If you bring your own phone, don't forget the charger lead and plug converter.
Luggage and bags:
Make sure you bring empty suitcases (Yes! It's plural!). You need some extra space for those trips to the local markets and bodegas.
Clothing/Shoes/Weather Gear: Swim wear! Feel free to bring some hiking boots ;)
Toiletries and Medical Supplies: Sun lotion (or block? depends on the time of year.) During the 'local winter' from December 15th to January 15th you might risk having the temperatur going below 20 degrees C... Bring Penicillin for your own precaution. Doctors can be hard to get for those small injuries/infections. I didn't get to use it though. It's just I tip I got myself...
Camping/Beach/Outdoor Gear: For the evenings you will need something to keep the warmth of the sun in with. Some short sleeved shirts or something. During the O'sunny day though you will only need yourself and your shorts.
Miscellaneous: Don't bring too much. If you find out that you miss something, you'll get it at a reasonable price at the weekly markets. Mostly Fridays/Saturdays. Depends on where in the area you are at the moment. It's fully possible to get to them all ;)