Oriental Trading has so much luau stuff - decorations, games, hawaiian leis...etc. Just looking through their website or catalog will give you a bunch of ideas.
But...we did do a luau for a spring staff luncheon one year. We served giant sub sandwiches and fruit kabobs. But the hit of the day were the fruit smoothies. We had a couple of blenders and tons of fruit (bananas, mangos, strawberries, etc.), ice and vanilla yogurt. We whizzed up fruit smoothies and the staff loved it.
We had hawaiian music playing in the background. You could play the limbo and see how the staff does. We gave each staff member a hawaiian lei as well.
Our school wants to do some kind of welcome back to school thing for the teachers and staff. They want to decorate the lounge in a luau type atmosphere. What kind of slogan or other things should we have?