This pilgrims advice on this topic was:
I walked the camino last year from St. Jean in June, and I had a 20L backpack that weighed about 16 pounds, or 7 or so kilos. I had everything I could imagine needing (including a jar of nutella, a Spanish-English dictionary, a Spanish fan… none of which I would take again). Sometimes I thought I had too much stuff, or that I wish I had brought something else, etc., and I often wished I had come across a packing list like the one I’m about to write.
Read all about the Camino de Santiago packing List here.