When trying to wear your office, size matters. Look for the tiniest device that can get the job done.
Choose parts with maximum connectivity. Look for PDAs and accessories that support Bluetooth, WiFi, GSM, dial-up, fax, printing, IR, Ethernet, serial port, and a wide range of memory cards.
Windows Mobile is the best operating system choice right now for a wearable office. It is a truly multitasking, efficient, powerful, full-featured OS with a tiny footprint. And it already runs most Office-related applications.
A PCMCIA hard drive is currently the most cost-effective way to add storage space.
Don't even think about wearing this setup past an airport screener. You'll scare the security staff, and they'll make you pay dearly. Instead, check the accessories in your baggage.