I feel sometimes lunch interview are more important, cause they can identify from the casual lunch if you're a person they want to work with on a daily basis. Behave yourself. Don't be nervous. Pick up the topics they like and try to find out if you have sth. in common with the mangers or interviewers.

You can definitely wear the same suit. I believe Cafeine mm also talked about this on this board. Yes, sure, a different shirt would be great. But you can also buy a suit, sooner or later in your work, you probably will need it anyway.

Good luck!