Rather than books, the following will get you far in the first few days of residency:
Know how to work the paging system - both sending and receiving
Know the hours of the cafeteria (if it isn't 24 hours)
If you aren't provided with one, carry a list of the phone extensions on each of your most frequently visited floors, radiology, lab and the pager numbers of your fellow residents
Know where radiological studies are placed after hours (ie, are they stored somewhere different than during the daytime?).
Know how to access the official reads on radiological studies
Know where the closest restrooms are on each floor
Keep a bag in the hospital (in the call rooms, a locker, etc.) containing some essentials: shaving materials, toothbrush and toothpaste, etc. An extra sweater will also be handy as sometimes the hospital gets cold.
Have a red pen to write down important information ie, stuff your attending tells you to do
Know how to get around the wards without actually walking THROUGH the wards. You'll be suprised at how much stuff will get solved without you being paged, however, if they (the nurses) see you, they'll often stop YOU to solve the problem. Be stealthy.