They'll basically give you the standard speach on what foods you should have, what to avoid, etc. Also will probably be a list of foods to avoid altogether after surgery, the stages of what foods you'll be allowed to have, protein requirements, vitamins to take, etc.
Journals really are good to see exactly how many calories are in certain foods/meals. Even some "healthy" options can be loaded with calories or carbs that aren't needed. I've always loved salads, but if I pile on croutons, use regular salad dressing, and other toppings my "healthy" salad just became as bad a Big Mac meal.
It's always tough to look at a food journal the first time. Just remember the chances are they've seen way worse!