My day before and day of for my best race were so atypical for me, but I was so f'ing fit, that it didn't even make a difference.
Day before I was at a family event in which I ate steadily throughout the day. Then I went to drive out to where I was racing and started having car issues. I eventually had a buddy of mine come rescue me and drive me out. I got to where I needed to go at 3am, and proceeded to pass out on top of my friend's bed.
The day of I woke up at 6:00am after 3 hours of sleep, and did a shakeout run around the block. I think I had a powerbar after the shakeout for breakfast. Then I dealt with the logistical nightmare of getting to a big, big city race, barely making it in time to do pre-race rituals. But the hay was in the barn, and when the gun went off, I ran out of my head and had an amazing performance.
Just goes to show that if you do the work beforehand, you could almost get away with anything the day before, and day of, and still have a good race.