One thing to keep in mind is almost EVERY new intern feels nervous about starting up, so you're not alone.
If you're really that anxious about it and want to be prepared, I think you'll do just fine reviewing the medicine portion from a Step 2 review book and focusing in on manegment. If you really want to narrow that down, try to review cardiology (especially how to read EKG's, treat MI's and CHF, etc...), review electrolyte imbalances, reviewing acute issues in GI would be helpful.
Also, you might already have it, but I think the best pocket book is the new addition of Pocket Medicine: The Massachusetts General Hospital Handbook of Internal Medicine (Pocket Notebook Series) (Ring-bound)
by Marc S Sabatine. This has served me very well this year.
With that said, I really wouldn't worry too much and think you might be better off relaxing before you start, which is what I did. Nobody expects you to know anything when you start. You'll learn as you go.