Hawaii is casual: sandals, bathing suits, and comfortable, informal clothing are the norm. In summer, synthetic slacks and shirts, although easy to care for, can be uncomfortably warm.
One of the most important things to tuck into your suitcase is sunscreen, though it is readily available at most stores.
As for clothing in the Hawaiian Islands, there's a saying that when a man wears a suit during the day, he's either going for a loan or he's a lawyer trying a case. Only a few upscale restaurants require a jacket for dinner. The aloha shirt is accepted dress in Hawaii for business and most social occasions. Shorts are acceptable daytime attire, along with a T-shirt or polo shirt. There's no need to buy expensive sandals on the mainland—here you can get flip-flops for a couple of dollars and off-brand sandals for $20. Golfers should remember that many courses have dress codes requiring a collared shirt; call courses you're interested in for details. If you're not prepared, you can pick up appropriate clothing at resort pro shops. If you're visiting in winter, bring a sweater or light- to medium-weight jacket. A polar fleece pullover is ideal and makes a great impromptu travel pillow.