I'll (as usual) tag on to JT's suggestion.

Take the shuttle to the Marriott. From there you can walk all around Nawiliwili (many shops, eats and a decent beach).

If you get bored there, walk towards the cruise ship pier (there's now a ship in nearly every day). From there you can catch shuttles to Hilo Hatties and K-Mart which is at Kuku'i Grove the main shopping center for Lihu'e.

Having done both you will have seen about all there is to see in Lihu'e town.

No where in Lihu'e are you more than a 5 minute car ride from the airport. Worse come to worse, stick out a thumb. Use some common sense, don't jump in with anybody who makes you even the slightest bit nervous.

Lihue1k