Thank you.
Well I have read the thesis again carefully making sure I understand everything, and have gone over the mathematical models in it. I have also read some of the key references in the thesis, to remind myself how my work relates to them and how it is different, extending knowledge etc. I have also found this thread http://www.postgraduateforum.com/threadViewer.aspx?TID=13794 very useful and have tried to prepare for the questions Koturu wrote. Finally I have tried to make summaries of the chapters in the thesis, main questions, hypotheses, main results and conclusions.
I am not sure how helpful this is, or whether this is the right thing to do but I guess I will find out tomorrow. I think it will be key to remain calm, and polite. Easier said than done :p