In addition to the below, you may like to take vaccinations if you haven't already done so, but it is not strictly necessary for such a short trip to a big city like Beijing.
I recommend bringing games/juggling items, frisbees (i'll bring some) things that may be fun to have but hard to come by in China.
Electric outlets are compatible with those in most western countries.
Before you Leave
Guide books and maps
Passport and visa(s)
Foreign currency of your destination country
Credit cards
Travelers checks or ATM card
Insurance: Trip Cancellation/Medical
Personal Identification
Photocopies of documentation
Basic Essentials
Appropriate Luggage
Luggage Locks & ID Tags (Do NOT Lock checked baggage)
Appropriate Clothing
Comfortable Footwear
Rain Protection
Camera and Film (Place film in carry-on baggage)
Laptop
Telephone Plugs for Modem
Small Flashlight
Travel Alarm Clock
Small Binoculars
Brimmed Hat or Visor
Reading Materials
Playing Cards/Games

Address Book
Maintenance Items
Batteries for camera and flashlight
Mini Sewing Kit (place in checked baggage)
Travel Iron or Steamer
Sink Stopper
Folding Scissors (place in checked baggage)
Laundry Soap Packets
Laundry Bag
Ziplock Plastic Bags
Medication
First Aid Kit
Aspirin/Pain Reliever
Cold/Sinus Medication
Diarrhea Medicine
Laxative
Insect Repellent
Contact Lens Preparations
Antibiotic Ointment
Alcohol Wipes
Sunscreen
Motion Sickness Medicine
Personal Hygiene Items
Personal Prescriptions
Toiletries
Comb/Brush
Toothbrush/Paste
Dental Floss
Shampoo
Blow Dryer
Deodorant
Lotions/Creams
Cologne
Lipbalm
Towelettes
Shaving Cream
Towel/Washcloth
Earplugs