I recommend taking Austrian economics. It is a fun class. The reading is quite different from the reading in your other classes and it will help you critique general equilibrium models in macro. Public Choice is also a good class, but it can be really technical and most first year students wouldn't be ready for it. Do not however, confuse goofing off with your study group with studying.
Many students sleep well at night thinking of the many hours spent with their study group.
Many of these students, however, will be generously donating their study carol and class space next year to someone else. You should have some fun, and some of your best memories of graduate school will come from late nights talking with your friends about some new and cool idea. Many people here read non-required economics as their hobby and as a way to help them remember why they want to study economics. If you don't know laissez-faire books, you should get on their mailing list and check out their web site. Many of the books that you will want to read are available there for relatively cheap.