Most items that you need will be pretty obvious, unless your mother still packs your bag for you!  But you will need to bring:

• lap-top
• adapter to Spanish sockets (Type C, F)
• camera and download cable
• walking boots
• wet-weather gear for walking (weather can be unpredictable)
• sunscreen lotion (easy to burn at altitude)
  
• warm sweater
• sensible hat for walking
• silly hat for evening entertainments
  
• credit card to pay the hotel
• cash (Euro) to pay for beverages
• pens and notebook