October-November is the hottest time of year in Thailand, with temperatures probably mid-80's F.
Pack lightweight, breathable clothing like cotton shirts and shorts with a warmer layer available for colder nights or after swimming.
Excellent and very affordable laundry services are available everywhere we go: pack clothing for 7-10 days and bring a little extra cash.
A wide-brimmed hat, sunglasses, and sunscreen are essential for protecting yourself from the strong sun.
Rubber bath mat: some hotels have slippery shower floor tiles.
Other ideas: Packing List reference and Thailand Travel reference