Langkawi is basically a 'duty-free' island. Which means booze and ciggies are really cheap. However, Malaysia itself is duty-free for other things (eg. electronics equipment and watches etc) and you'll be fine travelling anywhere else in malaysia if thats what you're looking for.
Unfortunately, Langkawi is one sleepy island. I would personally recommend Penang as there's heaps more to do there. Lots of food and happenings during the weekend too. almost 6 years ago