Just got done with 5th in Mich. You don't neeeeed any book b/c Harrison's (the only one you use there) is available online through Ross. If you want to get something, get Tarascon Pharmacopedia and Maxwell's Quick Medical Reference (both like <$10 on amazon) and will be super useful for the rest of your medical student career.

If you want to be a big spender, Standford guide to antimicrobial therapy($15) is a lifesaver since we didn't exactly have the best professor for antimicrobials (Dr. K) and you probably had the same person. The book tells you lots of stuff but the most useful this is which bugs are susceptible/resistant to which drugs. There is also Current Clinical Strategies - H&P Examination for $13 which again, since they did a fantastic job teaching us everything on the island, this is a good reminder of what needs to be done/said/asked. Good for miami students too since they'll fail 90% of you the first time.

All of those are all pocket sized things btw

Lastly, if you have a smartphone, get epocrates....when i spent a night in the ER shadowing, docs there were even using it occasionally to look up something they didn't know.