My suggestion would be to listen to the podcasts of Life of a Law Student (do a google search or search in the itunes store). I listened to all the ones for first year classes before law school started. It won't exactly give you a feel for the language of the cases, but it will give you an excellent overview of the law in those areas.
Its certainly not a substitute for reading the cases during the semester, but it certainly helped me hit the ground running since I had some feel for the contours of the law going in.
The idea of reading Pennoyer in particular, at this point, may only scare you off of law school! We read it for the first day of Civ Pro and I went in to the first day HATING that class. It ended up being one of my favorite classes. In other words, Pennoyer is (in my view) one of the more difficult cases, not really that indicative of what you will be reading, and can be offputting.
As others have said-enjoy the summer, you should be able to do everything you need during the year. The only prep I did was to listen to the aforementioned podcasts (while driving, walking the dog, etc.) and read a few fun legal books (The Brethern, Becoming Justice Blackmun, Supreme Conflict, etc.) and I was not ill prepared at all, and, FWIW, finished near the top of my class.
This will probably sound pathetic because I know I should know how, but how do I get those podcats on my iPod? I just have your standard Nano...
I see that there are MP3s of them all on the guys site. Can I just download those and drag them into my iTunes? I've never downlodaded a podcast onto my Nano before, I just watch them online usually.
Thanks for all the case suggestions. Again, I'm not trying to glean any great knowledge from them. I just want to get used to reading them.