Galicia is known for crazy weather... Personally, my "waterproof" pants did not work well and just made me cold during my hike.... Shorts worked much better than pants because drying time was much quicker!
I would recommend just having a poncho that covers you and your bag. I just used a deuter bag cover but the
Altus ponchos I saw other people wearing seemed much more reliable and convenient!
You'll be there for a long time... It's going to rain a little bit.... If you get caught in a thunderstorm without a poncho you will wish you had something that kept your stuff dry! If you don't get caught in stormy weather the poncho isn't exactly the heaviest thing in your bag...