Keep in mind, all of this advice is also not to be taken as an excuse to turn into a neurotic medical student a year before you'll turn into a neurotic medical student. All of the studying options involve you, your family, and evening television. These are things you should do whilst sitting on a couch watching football, or iron chef, or Spongebob if your kids are watching it. These studying concepts are about familiarity, not mastery.
First, there is Biochemistry. I hadn't taken it because it wasn't a pre-req and I'm was a Secondary Education major and former high school teacher. If you have not taken Biochem (one said they had) I would see about grabbing the required Medical Biochem text your school uses and start reading. You're going to be expected to discuss pathways and lectures will start with pathways on day one as though you already have familiarity. Build some familiarity. You don't want your first time pronouncing Phosphofructokinase-1 to be in your first lecture. I wish I had. I bought Lippencott's Review and it was pointless because it was a review text that assumed you already knew. Don't buy any review texts (you will eventually) buy actual text books.
Second, and I am at a loss for how to do this, but it would behoove you to learn about the various research techniques. I so bombed this and am still fuzzy on this, but my roommate, who did research for eight years, got every question correct on that block exam that covered that section.
Third, Seriously begin paying attention to nutrition, which you should anyway. My roommate is drowning in all these B Vitamins, fat solueble, water soluble, Omega Fatty acid, stuff. Familiarity with nutrition will pay off later.
Fourth. If you don't have any clinical experience, get some in a fashion other than shadowing. Take a CNA or an EMT-B class to get some basic medical knowledge and if you're lucky you'll get to see sick people. Regardless of if you are unable to obtain employment, those classes will be simplistic enough but also informative enough to start getting your feet wet. I already knew what a person with Jaundice looks like and I knew what Ascites was because I spent time working in an ER. It helps to have awareness.
Sixth. Start learning about health care issues and the system we will practice in. Health Reform is here to stay in some form or another. It'd behoove you to understand the differences between insurers, payors, providers, and patients. Those are basic fundamentals. In so doing, becoming aware of health issues now will just make it easier to transition in when you really need to know it. Think magazing articles, newspaper articles, etc. There is so much free knowledge out there that you can obtain in 10 minutes on Huffingtonpost, and Drudge by linking around.
Seventh - Anatomy. Find out what the required anatomy text will be and buy it. You might as well buy a Netter's Anatomy Atlas as well. Don't bother reading the text, just become familiar with all of the different pictures and disease states and the various clincial applications throughout the text. again, awareness is the goal here. You don't need to memorize anything, but seeing what sickness looks like so that your first time seeing what ascites in a belly looks like while on your couch relaxing and knowing you got in is a whole lot better than feeling like you just walked into a lecture in Japanese.
Netters is beautiful. The drawings are amazing. Find out what the path of Anatomy is at your school and start at the beginning. Look at the diagrams and become familiar with the relationships and the naming conventions. It wouldn't hurt at all to see how the muscles of the legs and arms attach and what they move. It isn't in a memorize a chart way, but in a look at the picture and see what it might do way. Seeing the complexity in the human body in a nonstressful way can allow you to appreciate it for a bit before you don't have time to appreciate it and you smell like formaldehyde.
This isn't a laundry list. It should not be taken as any form of a syllabus. It's me fishing my experiences from the trash and recylcing them for more than they are worth in hopes that it may help. If you have to triage the list, the biochem will be worth it's weight in gold. I spent more group sessions glossy eyed while my biochemist peers ran circles around the assignments.
Enjoy, flame, or whatever. I care not.
And lastly, and this one everyone should do who goes to a DO school..read The D.O.'s. Being aware of how not friendly the MD world is will keep things in perspective and allow you to understand what is going on when they look down at you. They will.