It's probably best to stick to going over your syllabus, introducing yourself to your students, and having them introduce themselves to one another. Since this is a workshop course, the earlier they get to know one another and feel comfortable discussing assignments together, the more smoothly your workshops will go in the future. If you have a Tues./Thurs. class and don't want to let them out too early, the PHG cookie exercise works well on the first day. It gives them some early practice with writing detail, they get to work together, and most importantly, you provide them with a tasty snack that will endear you to them for the rest of the semester.