Your group should produce 3-4 prototypes covering important aspects of your final game. I will discuss with individual groups about the specifics of what I'd like to see, but generally prototypes should solve some large portion of the game -- be it a tricky collision algorithm, a non-standard gameplay maneuver, interfacing a specific library, or just creating a certain art asset.
Ideally, each person in the group should work on a prototype that ties in with their role in the project.
We will view and critique the prototypes you create as a class. Each group will have 10 minutes to demonstrate and talk about their prototypes, followed by 10 minutes of questions.