I don't eat before going for an examination until I am done with it. Your lecturer was a kind person who allowed you go out, in my school, you dare not and once you do, that is the end of your paper, not even when you have seen the question paper. They will assume you want to go and cheat.

I don't know why Nescafe doesn't work for some people, I do take it when I don't want to sleep and it has always been saving me to complete my tasks for that night. I will have to force myself to sleep after then.