As far as clothing is concerned, it is in your best interest not to wear anything that is made out of cotton. Sure, cotton is really light and comfortable, but when it gets wet it becomes cold and heavy- and you will most definitely be getting wet while competing in this event. Try to select clothes that are made out of nylon or polyester so that it doesn’t hold water and it will be able to dry faster than other types of fabrics.
The fewer materials that you have weighing you down simply means that you will be able to complete the course faster and happier. Plus, whenever you have to adjust your clothing means you are going to be losing time that you could be running or climbing, essentially putting you behind.