The bandana is a classic clothing staple. Usually made of a light, cotton fabric, bandanas are square in shape and come in multiple colors with a black and white design in paisley or some variation.
Bandanas are associated with several different images. There's the cowboy, farmer and miner workwear and the hard rock band members of the 1980s who wore them as headscarves. You can read a great history of the bandana here.
One side note of caution: Be aware of neighborhoods you're in when wearing a bandana for fashion. In some areas, gang members or other affiliations wear bandanas of a specific color to associate themselves with certain groups.
Bandanas can be purchased pretty much anywhere, online, vintage stores and western wear stores. I actually have a bunch in different colors from when I was a kid growing up in Texas and going to the rodeo. You can style bandanas in a variety of looks. Here's one bandana, five ways: