On the morning of the 8th, Mayor Thomas will come by and remind you that they are all having a giant Harvest Festival event in Rose Plaza the next day. He requests that you bring some sort of food to be added into the soup. The next morning bring something edible to Rose Plaza. You can bring something you've grown on the farm or even a simple piece of colored grass. Give the item to Thomas and then you all get to sit back and eat your community soup. If you contribute something good to the soup, it will be delicous. If you give Thomas something un-soup-worthy, everyone will say how bad the soup tasted.