I used Dr Bronner's Peppermint Castile Soap years ago on my first long backpacking trip. It worked fine for a 15 day walk in the mountains, except that it
was still soap and I didn't really like the taste of it as a toothpaste. On my camino last fall, I took a bar of Ivory soap, which is what I use at home for bathing. After trying it once on my hair before leaving, it took two shampoos to wash out the sticky residue, so I also brought a small amount of my regular shampoo, and finally had to buy more in Santiago. I may just try to wash my hair less often on my next camino. I also took my usual laundry powder, which I thought should work, as I use it for hand washing as well as machine washing at home. But it would not dissolve properly in cold water. For this fall's camino, I may just use the Ivory bar soap for hand laundry, as I still had quite a lot of the one personal size bar when I got home. I took it in my regular plastic soap dish and it never stayed wet or went mushy after use. Or I may try out some cold water soap powder before I leave, as I have used that for hand washing clothes when travelling in countries where cold water is the norm. I think that for comfort it is helpful to use a soap that will wash out completely and not leave any sticky residue. Soap is a small issue in the almost infinite variety of equipment questions, but it can make a difference in our comfort, and that of those who have to live with us.