Dress is informal and relaxed on most occasions. Smart casual clothes are acceptable at most restaurants and -night-spots. Men are generally not expected to wear suits and ties, except in a few of the top formal bars and restaurants in major cities.
In summer a light jacket or sweater should be included in your luggage should the weather turn cooler or you visit the high country. You can expect some rain, so include a light waterproof jacket or coat. Pack warm winter clothing if visiting between May and September. Layer your clothing.