The headband. Now, this is not a fashion statement but a necessity for someone who sweats as much as I do. I have them in all kinds of colours and get a slight panic attack if I forget to bring one (sweat in your eyes, ears, nose etc is rubbish. RUBBISH!). For the same reason I also have one of those slightly ridiculous cycling caps under my helmet and an assortment of hats to run in if it's cold. Take that, sweat!