We recommend regular comfortable clothing. Although you can wear skirts, they aren’t recommended. We’ve even had people fly in full costume.
During the warmer weather, it is quite pleasant and refreshing. A lot of people love flying in bare feet. Other times, overdress a little. It’s a bit chillier at altitude (2 degrees C per thousand feet on average) and you are literally in the open air.
If you don’t wear prescription glasses then we recommend some kind of eye protection, like glasses or sunglasses (they won’t fall off :). Eyewear helps prevent watery eyes and bugs from spoiling your view. With the wind in your face you feel great. You are wide-eyed with the breadth and spectacle of the experience.