Portable applications, apps that follow you.
Although I am not that very much “working on the road” but do have a notebook is a need and yeah-fancy-too 
Previously I work exclusively in Windows platform so I bought a 12″ Centrino-powered packed with Windows XP and of course Linux Ubuntu for my ego.
All of my data including source codes are in sync with my desktop at home, so most of the time I use this laptop.
But at one time, I got an accident and the LCD was broken.
And since that time I left that poor thing home, pack important files into 1GB flash drive along with Miranda IM Portable for instant messaging, Thunderbird Portable for email, Firefox Portable for browsing, EssentialPIM portable for ToDo and Calendar, and TreeDBNotes Pro for outliner.
And I also put installer of Netbeans and Python, so if I happen to use a computer without them, I just installed.
I think there is Python portable named Moveable Python but I think it’s not free, then I stay back with source installer of Python and Netbeans + JDK.
That’s enough for my need, if you want another portable applications you can find at Portable Applications
But I think I still need a laptop, and since now I don’t use Windows that much (actually, Borland Delphi that keep me using Windows), a MacBook seems a good idea 
Java and Python run well in OSX
