Hi, I am about to set off for my 3rd pilgrimage next year and have done a few shorter walks in between. My advice is that the pack has to fit your personal frame most of all and be comfortable. If you use a raincape, you can have a non waterproof pack, otherwise a waterproof one or a pack which has a built in waterproof cover is best.
You can get a Lower Alpine 32 litre pack which weighs only around 600 grams, great for women.
It is waterproof. The
http://www.backpackinglight.com.au site has some great products. Their Roman Palm sleeping bag is the lightest I have found at 500 grams and sufficient for the Camino in Spain. On the Le Puy route gites have blankets and a sil bag is enough. Backpackinglight has the lightest rain cape I have seen at 140 grams. I personally used a Vaude Civetta 32 backpack, which I liked because of the many separate pockets. It has a waterproof cover and weighs just over 1 kg.
I have got my packing down to a minimum now, which really works for me:
Sleeping bag or sack
Lightweight but warmish fleece
Raincape or lightweight breathable Gortex Parka, which comes to just above knee, so no overtrowsers needed.
Lightweight but sturdy boots or walking shoes, waterproof. Shoes are sufficient in Spain, boots better on Le Puy route.
3 undies, 2 bras, 3 pairs of socks.
Merino first layer t shirt
lightweight wicking t shirt
long sleeved UV repellent shirt
Lightweight shorts
3/4 lenght or zippable pants
Lava Lava, great for going to and from shower/toilet or as a makeshift skirt while you dry your washing
Togs
Boxers to wear at night/but lava lava also good
Sunhat
1 metre of muslin to use as towel, much better absorption than synthetic and dries in seconds.
1 pair light sandals.
Documents and bank cards
Camera and charger and adaptor
Mini notebook
Pen
Spork, a titanium spoon fork combination, useful for salad, yoghurt en route
First aid kit with thread and iodine to treat blisters, plaster, bandage, antiseptic cream in mini tube, panadol, antihistamine
Emergency blanket
whistle
Toothbrush and mini toothpaste
Moisturizer with sunblock
Wondersoao for hair body and clothes
Waterbottle
Leightweight small bag to take around to go shopping for groceries or when you go for a swim or out for the evening and want to take a jacket and cape....
All this should weigh in around 6 kg, which makes for really pleasant walking.