Not a pile of washing..... but various base layers and socks to keep me comfortable.
There are two sorts of base layers. Thermal and cool. As the name suggests one type is best worn in cooler weather and the other when it is warm. Thermal base layers are constructed using marino-wool or synthetic thermal fibres. The best out of the two in my opinion is marino-wool. Not only is it warm and comfortable, but marino wool is one of the only natural fibres that allows quick moisture transfer, and retains warmth. During the warmer months then I tend to use coolmax fabrics to help regulate body temperature. Again there is nothing worse than hiking up a stream with sweat dripping off you. Apart from becoming a fly magnet, when the air temperature drops, so does your body temperature. This is where the base layer will help to keep you comfortable.
Right: Outer face fabric.