Laudanum or opium itself...
From Wikipedia:
According to Coleridge's Preface to Kubla Khan, the poem was composed one night after he experienced an opium influenced dream after reading a work describing the Tartar king Kublai Khan. Upon waking, he set about writing lines of poetry that came to him from the dream until he was interrupted by a person from Porlock. The poem could not be completed according to its original 200-300 line plan as the interruption caused him to forget the lines.
We operate like this: the "overseer process" tells the brain, using blunt instruments like chemicals, that we need to find something to eat, somewhere to sleep or someone to mate with. Then the brain follows orders. Unfortunately the orders we receive from the "overseer" are often wrong, even though they were right in the ancestral environment. It seems the easiest way to improve humans isn't to augment their brains - it's to send them better orders, e.g. using drugs. Here's a list of fantasy brain-affecting drugs that I would find useful, even though they don't seem to do anything complicated except affecting "overseer" chemistry:
1) A drug against unrequited love, aka "infatuation" or 'limerence".
2) A drug that makes you become restless and want to exercise.
3) A drug that puts you in the state of random creativity that you normally experience just before falling asleep.
4) A drug that puts you in the optimal PUA "state".
5) A drug that boosts your feeling of curiosity. Must be great for doing math or science.
Anything else?