Well, I'm newly banded so I don't know too much about this whole thing, but I can tell you what I do know. I was put on a very strict diet 2 weeks before my surgery. The purpose of the diet is to shrink your liver so that the doctor can access your stomach easier while banding you. IF you do not shrink your liver enough the doctor will close you back up and not do your surgery (some food for thought).
Like you, I've had a life time of bad eating habits and giving in to cravings...if I saw it, wanted it, I ATE IT. The thing that got me through the whole process was this line of thinking "whats more important...eating those tacos your love or becoming a healtheir you". I chose to be a healthier me. I know its hard but if I can do it then anyone can. I learned its all about your mind set and how you view what you are doing. Everytime I wanted to cheat I kept reminding myself WHY I was doing it and what it was that I wanted to accomplish. I hope this helps you.