Yea, definitely eat light the night before. Intestinal distress during the exam can be very detrimental... And embarrassing, LOL.
The key is to eat the right breakfast before the test. Load up on complex carbos so you will have the energy to last the day. Grab some nice hash browns for breakfast and add a cornbread, some coffee for the caffeine kick, but minimize the refined sugars.
The complex carbos will take a while to digest, keeping your blood sugar constant throughout the morning, rather than the 15-minute high and crash of refined sugars (sweetened cereals are the worst offenders).
Methyl xanthines (caffeine) will keep your energy metabolism high and make you more alert.
A Trail Mix bar or two during breaks (if allowed by the proctors) can do wonders for stamina during the last few desperate hours too.
Worked for me, obviously... 😀