If it is only ONE thing, it has to be something to drink. In my case it would be just water.
Chess and gastronomy
Sort:
Marshmallows.
A cow
my opponents time
A meal. As for the time, start at some arbritary time before the tournament, preferably a few weeks before and finish sometime afterwards.
If you could only consume one thing within 24 hours before an important chess match (that you were playing in), what would it be, and how long before? This can include food, beverages, vitamins, herbs, supplements, drugs, etc...