It depends on what rotation you are on
IM: The medicine docs will walk around with 3-4 textbooks, a hundred and fifty patient notes, 35 pens from every pharm company, two stethoscopes (a spare one just in case), their flash drive around their neck, 4-5 badges for every hospital they have privileges.......... you get the idea
surgery: Most surgery docs carry just a pen - some of the hardcore ones are still wearing their scrub caps from their first Whipple, others usually just keep 1-2 in their coat pocket. If you're on call in the ER though don't forget the trauma sheers, with the hemostat just incase you find a bleeder when cutting off their clothes.
Ob/Gyn: A date wheel for their pregnancy, and the latest edition of "OB-Gyn Secrets, how to survive the malpractice suit you most certainly will be involved in". Also carry a good reference book because nothing in ObGyn makes sense, nor will it stick.
Pedi: A good little handbook with great information for pedi patients - Its called "Kids are basically little adults". Also carry a ton of stuffed animals. If you can get it to wrap around your stethoscope - you get HONORS!
Neuro: Your reflex hammer, tuning fork, to test sensation, you'll need something soft, and something sharp - the something sharp can also be used to poke your eyes out if you can't get through the 3 hours it takes to do a full neurologic exam
Family Med: Carry a PDA - for some reason they love to use PDAs. You can play solitaire on it for all they care, as long as you're using it. Also, carry multiple copies of the following two handouts - first is "Your viral URI, why you DONT need antibiotics" and second "For the love of all that is holy please keep taking your HTN meds"
Psych: Don't wear a tie - apparently the patients can use your tie to their advantage (they are creative). Carrying a copy of the DSM-IV is a great idea, so you can be sure to rule out depression on the patient who's only been experiencing symptoms for 13 days
Sub-I: - Leave your dignity at home - you are the full-time scut monkey. Keep copies of skeleton notes and blanket orders, should save you some time and let you squeeze in 30-40 mts of sleep when you're on call q2.
Honestly, though, on your first day show up with your steth, a pharmacopia, a pen, and a good pocket book for that rotation. From there add and remove what you need - each rotation is different. but remember, its best to travel light, your body will thank you for at the end of the year
good luck