You don't need a whole pig roasting in an underground pit to create a fun luau themed party, but it doesn't hurt. Although this may be a bit much for most casual hosts, some other traditional luau staples will work just fine. You can offer the ladies grass skirts and faux leis to wear. Both are available in bulk at reasonable prices. The men can wear leis and sport their own brightly colored Hawaiian shirts. Tropical fruits are a very nice decorative touch here, too; in large bowls, they'll contribute interest and fragrance. Filling your house or deck with ferns, bird of paradise, orchids and other exotic flowers and plants will help to create a tropical mood that's textural and dynamic.
This is another occasion where a raffia table skirt will come in handy. Ukulele music can help carry through the theme, so will bowls filled with macadamia nuts. As a novelty, display coconuts with a few cut stalks of sugar cane. They'll add an unexpected and authentic touch.