in the morning have a fruit smoothy or a fruit with your breakfast. id advise you to have cereal that is filling like porridge.. it really keeps you full. stay away from sour stuff. make sure you have a full lunch that cover all nutrients and same goes for dinner.in the morning try do stretches and basic exercises for 30 minutes then start your day. eat dry fruits like almonds. etc. you can buy a packed of dry fruits which you can nibble on while you are revising. and make sure you do a number 2 in the toilet everyday :P
good luck for your exams.