Well... here i am! Im a great fan of the books of Castaneda. Ive read the 5 first ones, The teachings of Don Juan, A Separate Reality, Journey to Ixtlan (the best in my opinion), Tales of Power, The Second Ring of Power and the last one, The Active Side of Infinity.

I believe its not fiction. I think no man would just create all that knowledge and wisdom. I really believe Castaneda had a teacher who teached him about that deep knowledge. And, even if the history of the books were fictional, the knowledge in it is not, as much of it is present in some religions, or beliefs, and even in the things called sorcery, or magic.

The little smoke's known hallucinogenic component is a Psylocybe mushroom, as stated by Castaneda. Maybe there is some salvia too in the smoking mixture, but if so, its not mentioned by Castaneda.

In my opinion, weed is a plant of power too. Not too powerful as the another ones, but yet it alters the consciousness, and helps in things as stop the internal dialogue, not-doing (as it increases the capacity of gaze at the things), helps sooo much the controled folly, and lots of another things i dont remember right now.

For somebody that never did read any of his books, i would suggest to start by the 3rd, Journey to Ixtlan. In this book Castaneda talks about the "phylosophical" knowledge teached by Don Juan, and for me its better to start there. After it, reading the 2 earlier books will make a lot of more sense.
Even cause they are more orientated to the psychedelic experiences, and it was only in the 3rd book that Castaneda realized the role of the plants of power only as an aid, and not as the major way to understand the Don Juan's teachings.