The first day of any class often sets the tone of the whole run of the course. That's the time when teachers get to introduce the students to what the course is really about. What are the expectations the teacher has for the students? What are the rules students are expected to follow? And most important what will the students be learning? And how will things be taught?
Leigh Ann Sudol (I talked about her yesterday) has a post in the Computer Science Teachers Association blog last week where she talks about one of her favorite first day exercises. She has students write the directions for a paper airplane and then has them switch so that others try to follow those directions.
That's one of my favorites as well and I've used it for years. It shows students just how complicated giving instructions can be. Leigh Ann asks for other first day suggestions on the CSTA Blog and I hope others drop some by in the comments or in their own blogs linking back to there.
Which reminds me, a first day exercise that was used in a class I took a long time ago used writing instructions for tying shoes. Writing directions for that task without using pictures can be quite a challenge.
BTW I highly recommend the Computer Science Teachers Association to all teachers of computer science. If you teach computer science it is worth checking out.
[Note: There are a number of interesting suggestions in the comments of the post at the CSTA Blog. ]