I do a good amount of caffeine, L-theanine, Ceylon cinnamon and Hericium erinaceus mushroom.
Those paired with a very antioxidant based diet make me a working machine. I can easily churn out 12+ hours of focused work daily with very little sleep.
Most definitely not healthy - can't recommend to anyone - I just happen to be a bit smooth on the brain and want to sacrifice my health for money.
I also do get nicotine in the form of cigars in the summertime. I do feel more productive after I've smoked one, but haven't made the decision yet to start taking nicotine as a nootropic - perhaps in the future.
All that is fun and all, but the best way to keep yourself mentally sharp is to just sleep well, exercising frequently and having a...