>>88881A Buff, it's a long cloth tube that is surprisingly versatile.
I've used mine as a bandana, dust mask, sweat band, balaclava, beanie, sleeping mask, a neck cooler and even a small stuff sack (just tie both ends shut).
The basic buff is made of microfiber coolmax so it breathes well and doesn't cling. They also have ones that are UV rated, ones that are pre-treated with insect repellent and merino wool ones as well.
I've had mine for 5 years now, goes with me every time I step /out/.
