Smoking marijuana
I like to plan my stuff when I'm high because it put me in some of the most interesting adventures I've been. If you are a daydreamer, it is also good because you will have more fun with your wasted creativity.
I think I tried doing some code when in Amsterdam in a coffee house ... with this super high hope that it was going to be great. IIRC, I couldn't think at all. Zero productivity.
But that could have been a consequence of the "setting" rather than the drug. It would be cool to try out coding when high in a THC cowork space in Amsterdam specifically designed for people coding on laptops when high. That could be some hackathon!
I feel really easy to get into the "zone" (or how you call it) programming high. And I usually find clever solutions to problems I'm stuck too. Also, if I'm totally not in the mood of programming but I have too, a joint sure helps a lot.