Backpack-type carrier (usually)
Sony laptop
iGo Juice power supply with auto/air adapter
hearing aid (don't usually wear it)
hi-intensity compact flashlight
RF presenter's mouse (if I'm going to be presenting on arrival)
blank CD-Rs
pens
business cards
travel wallet with passport, hotel/airline membership cards, boarding passes, one credit card, and an emergency supply of cash
paperback book and/or magazines
legal pad
noise-cancelling headphones
RJ11, RJ45 and sync/charge cable for Treo 650, all retractable
couple of spare AAA batteries
Zip-Loc bag for going through security (pocket contents)
anything I plan to eat on the flight

in pockets or on belt: Treo 650, 1GB Lexar JumpDrive, change, wallet.

All that is if I'm traveling light . I've been known to add a second laptop, a digital camera, a video camera, and/or a battery-operated printer.