Packing list
Have a look at the CSJ page
http://www.csj.org.uk/planning.htm which has a good packing list. I would not bother with their optional items but 4 things I would not go without are:
1 A pillowcase (a clean pillowcase to use with the pillows in refuges or fleece from your pack weighs very little and gives a clean place for you head each night, you can also use it as a hat)
2 A tiny torch (a very small torch or head torch is useful for the early starts it is wise to make in summer to walk in the cool of the morning)
3 Earplugs (after your first night in a refuge you will realise these are probably the first thing you should pack)
4 A mobile phone (many pilgrims have a prejudice against mobile phones but I think they can be useful in emergencies, for booking rooms in hostales and hotels for a little luxury and for security for those walking on their own).
Buen Camino
William