There are various kinds of luau food. Namely poi which is made from the Taro root. Also Kalua Pig which has been cooked in an underground oven known as an imu.
Here is a short list outlining some of the dishes you should expect to see at a luau:
Ahi - Yellowfin tuna.
Chicken long rice - chicken with long grain rice.
Haupia - coconut pudding, the consistency of jello!
Kalua Pig - Roast pig, very juicy and tasty.
Lau lau - spicy vegetable, pork, or chicken filling wrapped in taro leaves.
Lomi lomi salmon - A spicy raw fish and tomato dish.
Mahi mahi - The colorful dolphin or dorado fish, named for its fighting ability (mahi means "strong").
The meat is moist, white, and has a mild flavor.
Namasu - Pickled cucumber salad.
Ono - Tuna.
Pipi Kaula - Hawaiian-style beef jerky.
Poi - A bland whitish to purplish paste made from the root of the taro.
Poke - Seasoned raw fish.
Sweet potatoes - A yellow slightly less sweet version of the orange mainland cousins.
Taro - This plant is made into a sweet purple bread, poi, boiled, fried, or baked.