a nice summery outfit is a pair of beige or light colored shorts and a dark collared shirt.
if it was something more formal, your obvious dress pants and dress shirt, but not when it's something casual.
questions you should know the answer to are:
what are your long term / short term goals
what do you want to do with your life / where do you see yourself in 10 years
why do you think you'd be a valuable member to a team
describe yourself in one word, explain
what are some of your best / worst qualities
and then your typical:
explain a time where you had to be a leader or take on a leadership role
explain a time where there was a conflict that you had to resolve and how you went about doing that
explain your prior work experience with people / on a team
explain any community involvement and what position you had in that
even if these questions aren't asked directly, you should find a way to throw them into an interview and discuss why you're a confident person with ambition and positive qualities, etc etc.