Don't know if this helps, but when I was taking night college classes (full of nurses - don't ask), the nurses swore by eating pasta and drinking purple grape juice the night before before taking an exam.  Something to do with body stamina and brain power.

Worked for the nurses who had to re-assemble a model of a human brain in X minutes.  Although the non-medical students like me wondered, "Why would a nurse have to know how to put our brain back together? Does this mean if the doctor isn't around, the nurse does it?"