I have saved every shampoo and soap from every hotel I have stayed in for the last 20 years, and except for the occassional replacement for the extra set I keep in my toiletry kit, I haven't used any.
I have literally hundreds of these single serving versions, plus mouthwash, shower caps, shoe polishing rags, toothbrushes, etc.
I also bought a book on soap and candle making, it's in one of my bug out bins, I recall glycerin being a prevalent ingredient but forget where it can be obtained off grid.