FWIW, I think figuring things out from the casebook is an important part of the whole process. I don't start using supplements (and I only use treatises/hornbooks because E&Es are dumbed down and thus not helpful for complex exams) until about 3 weeks out from the exam.
There is really no point in stressing out about it over the summer. The people who will "get it" first year (I'm not necessarily talking about the material) are going to "get it" and an E&E over the summer isn't going to help make you one of the students that "gets it."
I've recommended the same two books - and only two books - for summer prep over and over again that may help you "get it." The other thing you can do is become educated about the job process and start drafting cover letters and researching firms.
More work doesn't necessarily mean better grades. Knowing more on day 1 doesn't mean better grades. I got a 3.9 in the class I didn't bother making an outline for.
I agree with Yellow's entire post here. I think most of the time, the BLL can be found in the case. The courts usually don't hide it. I don't think I'm necessarily better at reading than most people, yet I more often than not have no problem finding the rule of law a court applies in a case. (big exception is often Con Law cases - the Supreme Court often doesn't know what it's doing, and even if it does, I think they like to "hear themselves talk" when they write, so rules can get buried.)
I also think that finding the law within the cases is a very important part of the whole process of school - I mean, when a senior partner gives you something to research or a client comes in with a problem, you may be able to go to a practice guide or something and get some guidance, but a judge may not give a damn what Corbin says on Contracts - a judge wants to know what the rule of law is in YOUR jurisdiction, and you find that by reading the cases.
Like Yellow, I also used supplements almost solely in exam prep and review, after you know what your professor thinks the law is. When I used them outside of/before exam prep, I would do so AFTER class if I was not getting something.