Frankly, I did nothing to prepare except made sure I bought the right books for classes and made sure I knew how to get to each of the classrooms. I didn't read any of the books on that summer reading list, although I'm sure some of them might be interesting or helpful. I spent most of my last free summer at the pool, and I haven't suffered in law school for it.
I worked two jobs during my first year, so any extra time I got from being a part-time student was spent at work. I can't really speak on what it would be like to be a part-time student without a job, although I know that some people do it that way.