Nothing seasonal is running in Kuala Lumpur & the west coast in September — which is its own answer. Pack for the temperature.
Going in October
The wettest stretch of the year on this coast, peaking in November — afternoon and evening thunderstorms most days.
What this means for your bag
A packable rain shell
Not a winter coat — it stays warm through the rain. A light hooded shell that folds into its own pocket ends up in the day bag instead of the hotel room.
See the Weather Protection packQuick-dry fabrics
Cotton takes two days to dry in this air and starts to smell before it does. Synthetics and merino wash in a sink and are wearable by morning.
See the Summer Sun Kit packA layer for indoor air conditioning
Malls, buses and restaurants are cooled far below the street, and the swing is what makes people ill. A light long sleeve doubles as sun cover and as dress code for temples and mosques.
See the Smart Casual Evening pack
Build a packing plan around the season you are actually travelling in.