My number #1 is sleep. I am completely a different person with 8+ hours of sleep. I can track it using lichess puzzles. It gives you an elo score against the puzzles. I fall in a 250 point range depending on how I have been sleeping.
#2 is how much I am eating. Staying slightly hungry is best, but hard to do.
oh yeah, sleep is really important for cognitive performance. i discovered this in detail when i had access to amphetamine while i was working on code. i found that if i restricted my use of the amphetamine so that i got a good 8 hours i was consistently productive. if not, by the next day (after not sleeping) i'd estimate i was at 25% of my capacity. i tried to explain this to my friend, but he tended to snarf and snarf and snarf until he started displaying tourettes symptoms and this weird, psychotic dark streak that was not in his normal repertoire. he never listened to me, but i was always happy when there was some amphetamine in the lab, i did my best work during those times.
