Tryptophan.
'Scuse me, I’m sleepy.
Just to be different, I’m going to say Cysteine.
It forms disulfide bonds, essential for proper protein folding and structure.
According to wikipedia, it supports the conversion of acetaldehyde to acetic acid, reducing the toxicity of alcohol – what could be better than being able to tolerate more booze?
N-acetylcysteine is a handy little molecule which is used as a mucolytic, or to treat Tylenol overdose, or to protect the kidneys from IV contrast agents.
The Exocyst scared the beejezus out of me when I was a kid, but now I really like it.