Put fuel in the tank!
Keep topped up by drinking plenty of water whilst you study. Make a rule of keeping a coaster on your desk to remind you. Always have a water bottle nearby!
Fizzy drinks do you no good when it comes to brain power. For all the short term energy you may think they give you they're not part of the Exam Coach Way to achieving great results. The same goes for chocolate and sweets! As a general rule consume all sugary foods in moderation, don't rely in them for short term energy.
Water and healthy foods are the way forward and they are the fuel your brain needs to deliver the results you are capable of.