Let's see. In my bag (LowePro laptop bag), you'll usually find:

Laptop (Thinkpad T40)
iGo Juice power supply with three PPS cables and tips for cellphone, PDA, BT headset, and generic USB tip for iPod.
iPod (with iTrip for rental cars and a cassette adapter if they've got a tape deck)
Shure e3c earphones with tri-flange tips
A mini-sleeve with 6 DVDs (if it's a long trip, more will be in with my clothes)
A little gooseneck LED light I got at Fry's that runs off USB, 3xAAA, or cigarette lighter port.
A couple of books (again, if it's a long trip, more in my main bag)
A little camera (Casio Exlim) for business trips where I might get a little sightseeing
Motorola v600 quad-band phone unlocked
HP iPaq 3850, maybe with Bluetooth expansion pack.
aluminum clipboard cover and a few file folders for work stuff
Pens/pencils galore (since I always lose them)

All of the little stuff is kept in 2 United business class amenity kit bags, which are perfect for this sort of thing.

If I don't know where I'm going, my Magellan GPS with serial/USB cable to hook into the laptop for maps.