From High Beam Encyclopedia:

King of the daily specials in Hawaii’s traveling lunch wagons and hole-in-the-wall eateries, the Plate Lunch is a strictly local phenomenon~~as Popular as the Hula and just as much fun to try! Often billed as the “Workingman’s Special“, it is never gourmet. But at its best, the plate lunch offers a hearty sampling of homestyle Island cooking. Entrees celebrate the gastronomic variety of Hawaii’s many ethnic groups: from native Lau Lau (pork wrapped in taro leaves), Korean Bulgogi (beef marinated in garlic/teri sauce), and teriyaki chicken (also called teri or Shoyu chicken)! Two large scoops of rice are to Hawaii’s plate lunch what French fries are to the Mainland’s hamburger. Rice is accompanied by an equally impressive scoop of macaroni salad (Grandma’s famous homemade Potato/Mac), which, along with an entree, forms the fundamental PLATE LUNCH! Combination plates are popular. “MIX-IT-UP“! Add your own hot sauce (Ask for Grandma’s Homemade Korean Hot Sauce! spicy & garlicy!) and shoyu (soy sauce) at the counter. “Lunchtime Tradition“- Usually served on paper plates or plastic foam trays, true plate lunches carry on a custom that goes back at least to World War II. Old-timers think that the bento–a cold box lunch that Japanese workers carried to the pineapple and sugar cane fields–was the inspiration for the Plate Lunch (many places still offer a cold bento take-out lunch). During the war, entrepreneurs in homemade lunch wagons adapted the basic bento into a hot meal to feed round-the-clock shifts of waterfront workers. Since then, this substantial but inexpensive fare has become a lunchtime staple of Hawaii’s blue-and white-collar workers. There’s a wider choice of main courses now, and most of the Japanese garnishes have disappeared, but the basics have changed little over the years. Highly portable and wrapped to stay hot, plate lunches are especially popular with Islanders for impromptu beach or park picnics. You dig in with chopsticks or a plastic fork. Wash it all down with soda or tropical fruit juices.