As we all know the weather can change even when you are out on a cycle so this is difficult to answer. Look at the weather forecast a week before then start packing your kit. Arm and leg  warmers are always good to carry as they are small and take up little luggage space. I always take a waterproof but wear it at the airport as it saves bringing too many jackets. Remember you will have free washing kit bags and washing facility at the hotel. Wash in the evening and your kit will be perfect for the next day.