For people to visit U.S. from China, I guess the following items are necessary to survive. I am trying to keep this list as short as possible and only list the most important stuff. I will ignore obvious things like cloth and passport… This list applies to those who travel from U.S. or Europe to China as well since the difference is in two directions.
Travel Plug Converter
Not only the voltage differs between China (220 Volt) and U.S.(110 Volt). So do the shapes of the outlets. Most electronics we carry outside the country were designed to tolerate wide range of electric voltage, such as laptop (at least my Dell laptop) and mobile phone/digital camera recharge, but the shape of the plugs and the outlet may not be compatible. This is the model I brought with me to U.S.

Image credit: Planet3000
The plug of my laptop is for use in China only with the shape of this:
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Although I don’t need a voltage converter, I still need this otherwise my plug cannot connect with the outlet. This is also the first time in my last four U.S. visit that I prepared this in advance. In the first three trips, I always need to spend 1 or 2 days looking for this small, cheap but important stuff.
People in U.S. traveling to China may also consider this issue.
Calling Card or Mobile Phone
It is critical to have a calling card or mobile phone with you when traveling in U.S. To use the coin to call back home is just too expensive and inconvenient.
I brought my mobile with me and it worked very well. The Dopod 515 with me. It is a tri-band mobile. China is using band 900/1800 MHz while U.S. is using 1900 MHz. After I arrived in U.S., I changed the setting to 1900 MHz (note: it will not change automatically) and then I was using wireless service provided by local providers. I have experienced Cingular, AT&T and T-Mobile during my stay. I didn’t use the phone though, but to some device with you that you can turn to during emergency gave me a sense of security in foreign land.

© Jian Shuo Wang. Cingular on my mobile
Be sure to call 1860 to open international roaming service first. It is free.
English Translation of Driver’s License
Although not required, it is much more convenient to have an English copy of your Chinese driver’s license if you plan to drive. I translated it myself and print it out with a normal printer. It helped because there is no English on the license.
Credit Card
This needs special note that not all cards issued in China can be used online or aboard, even it has a Visa or Master logo. My China Merchant Bank International Credit Card worked great. Now the good thing is, I can pay with credit card with USD and deposit Chinese Yuan to keep the balance. I didn’t exchange US dollars for this trip. Before, when USD was hot, people always take the chance to exchange as much U.S. dollars as possible (2000 USD limit) because it is the only chance to exchange U.S dollars by Chinese Yuan.
More…
If possible, instant noodle may be a good choice just in case. I regret that I didn’t bring some when there is nothing to eat at deep nights. We have rushed from the White House area in Washington, D.C. to China town (via metro) and bought instant noodle in 24-hour CVS there and brought it back to hotel at around 12:00 in mid-night. All restaurants were closed, according to the hotel receiption. We didn’t expect this and assumed restaurants open till deep night.
Is there more stuff people needs to go to US? Please suggest.