Can an energy drink or chocolate before an exam be useful ? What sort of other edible goods be helpful? At the end of a session, we have to give an examination where 2 years worth of syllabus is asked and it is the most important examination. It takes place in 2 sessions 9-12 and 2-5. I have heard from some of my peers that having things like energy drinks or consuming chocolate could help boost the performance, while others tend to thing it's useless and might even have a negative effect on our performance. We get only 1 shot at this exam and I don't want to take any chance with it. So what I want to ask is, 

1) Can consuming energy drinks or chocolate have any effect on my performance (Positive/negative)

2) Are there things whose consumption or general recommendations which can boost my performance on the final day as after giving a 3 hour paper is quite exhausting mentally and physically. And also since it's lunch time, the type of food that I should consume (eg should I have more carbs to get energy or will it make me feel sleepy ??)
I think doing such things may be risky. Instead, do something natural. The most important is to get plenty of sleep the night before the exam and don't try to cram up to the last minute. 

Between the two exams parts, get some light exercise and, again, don't cram. Let your mind relax and let it integrate what you know rather than trying to force it to absorb things that may mask other, more important things. 

As for food, eat as you normally do but nothing heavy that will make you groggy and wanting an afternoon nap. If you eat differently, your gut may rebel against you. 

If you have been taking good notes throughout the learning period, then summarizing them on note cards (big ideas only) in the week previous can be a good plan. You can then do a light review at the morning and mid-day meal. A light review. Big ideas. 

But make your body and mind as comfortable as possible. Breathe deeply. Relax your face. Smile. (These are martial arts advices, actually.)