It's really about preparing you and giving the discipline before you start this journey. You will have a much harder time coping with the surgery if you cheat now. I know a good amount of people who cheated and did fine with the surgery. It is all mental, your going to have that headache and lightheaded feeling after surgery only you have no choice but to fight through it, I know your surgery is tomorrow but today just reflect on your relationship with food and try to prepare mentally. I am only 3 weeks out and I will tell you the surgery does not get rid of that mental hunger, so remain positive and focus on other things and you will do great.