I knew from the get go that I was going to be a stamp addict, so bought 10 in SJPP. The SJPP version is much more durable (heavier paper) than the standard Spanish version. They also provide a plastic zip lock type bag for each. I filled seven and part of an eighth. I was in Santiago for two weeks as a volunteer at the Pilgrim Office, so I decided to fill one with stamps from all over the city.
The following is a website that shows available sellos from several of the Caminos:
Www.lossellosdelcamino.com
I also sought out post office cancellation stamps. Hindsight being 20/20, I should have bought a postage stamp and stuck it in before getting the cancellations. Other favorites I looked for were town halls (ayuntamientos) and Guardia Civil police headquarters (in larger towns).
The big problem was the ubiquitous CERRADO sign. Some of these facilities have VERY limited hours - even in the larger towns.
Happy collecting