One of the major foods prepared and eaten during the Chuseok holiday is songpyeon (송편), a crescent-shaped rice cake, steamed, with crushed sweet pine nuts inside. The rice cake is found in many different colors but in my experience they all taste very similar.
Other foods commonly prepared are japchae (noodles), bulgogi (beef) and fruits.
Chuseok is such major holiday in Korea that is even celebrated by Korean people in the United States. I personally do not celebrate it with my family, but my family does enjoy eating seongpyun to participate in a small way.
I would love to go to Korea and experience Chuseok first hand someday!