If I have learned anything from living in foreign countries it’s that it is very easy to be unprepared for your experience… you are going to need a travel backpack. Inversely, you do not want to fall into the trap of being over prepared. I learned that lesson when I shipped my entire PC and monitor set up to Rome for a two month stay. Depending on how long you are going to be spending out of the states you are going to want to either activate your phone in the region you are traveling to or simply buy a prepaid cell phone or as they say in the spy movies a “burner”. If you are traveling strictly for business and you have clients depending on you I recommend that you shell out the extra coin and activate your phone. But if you are traveling for pleasure but still working from your hotel or apartment just buy the prepaid phone. What I do to keep my work informed about my current number is I create a spreadsheet and share it with all of my co-workers. The spread sheet outlines which country I am in and what number I can be reached at.
Another thing to keep in mind is how much time you are going to be spending inside the metropolitan area. If you are planning to spend most of your time traveling outside of the city that you are centrally located in it is smart to purchase a high quality travel backpack. I personally recommend Deuter, they make solid backpacks with a good warranty.
Finally, I would say just pack the essentials. You will need good clothes for any climate (check the weather online), enough technology so you are not completely cut off, and some good books. So many times people will travel out of the country and try to bring their home with them. You need to immerse yourself in the actual culture today not the culture of yesteryear. So leave the travel books at home and don’t be afraid to talk to locals or other Americans that have lived in the city for a while. Most Europeans can be a bit put off by the friendliness of Americans but don’t sweat it… its part of the experience.