I personally do not think you should look at material you have yet to cover (i.e. start reading all of BRS Pathology or RR Pathology). I don't think that would be beneficial to you nor would it be the best use of your time. However, once you begin second year, I would absolutely read RR Pathology along with each of your blocks. This will ensure that you at least get through RR one time during the year, and can get through it again during board time. I haven't sat for the Step yet, but I think RR Pathology is a highly valuable book.
If I could do it over again, I would still do the research that I did, but I would absolutely add on Gunner Training. Since I am currently studying for boards, I am quickly realizing the importance of first year topics that I considered (at the time) to be low-yield. I was wrong. If I were you, I would absolutely nail down pharmacology basic concepts, microbiology basic concepts, physiology until your eyes bleed, pathology basic concepts, etc. You don't need to do a systems-based approach to your summer studying. You simply need to ensure that you have the basic concepts down solid and that you feel comfortable adding new information to that base. You will be swamped with so much pathology during second year that I (again, personally) don't think summer pathology studying of yet-to-cover material would be the best use of your time.
I loved pathology second year. It is my absolute favorite subject to study, learn and read about. It is also widely considered to be the most important topic on Step 1. I wish I had re-read the basics before I began my systems-based pathology classes second year. It wasn't that I really needed them to understand the material (and many times I didn't), but I should have refreshed myself on these, especially now that I'm studying for boards (pathology core concepts regarding cellular injury, cell death, inflammation, etc. are definitely important). For example, certain disease processes cause specific types of inflammation, and when reading a question stem, you can easily rule in/rule out various disease processes based solely on the type of inflammation.
Bottom line: The things I would do differently if I could repeat MS-1/MS-2 summer:
1. Buy First Aid: this is not to study First Aid. Actually, I wouldn't even let any of your classmates know you bought it. The only thing I would have used it for would be to run through the chapters in the front and make sure I knew all that they were talking about in those chapters. This is to make sure that during dedicated board studying time you aren't trying to actually learn things you never learned the first time. Looking through First Aid early on should allow you to recognize things your school didn't cover during your first year and ensure that these things don't go unnoticed until your dedicated board studying time.
2. Gunner Training: No, I never actually did it. I took the free trial and should have signed up, but I'm cheap. From the raves GT has received on SDN, this will really help enforce those basic concepts from first year.
3. Read any other texts for first year material. Again, personally, I would not recommend attempting to cover any material you have yet to learn. This is for the basics.
4. Do research or something to pad your CV (I did this, but I am just reiterating its importance).
5. Rest.
Sorry for rambling and I hope this helps. I think boards is so important that I want to give honest advice to those who ask what they should do. This is an honest appraisal of what I wish I had done differently, and I hope it helps you figure out what is best for you to do.
MrB