I use KeePass to store my passwords and I need access to my passwords everywhere I go. KeePass portable allows me to do just that. I simply save the application on my USB drive and I'm on my way. There are many applications which have "portable" versions. KeePass, Notepad++, FireFox, Thunderbird, Sunbird, OpenOffice, ClamWin, 7zip just to name a few. PortableApps.com takes this idea a step further, they have compiled a large list of portable applications and have built a framework to consolidate them into a neat little package. After installing the PortableApps Suite on my USB drive, I have a single executable StartPortableApps.exe which opens a "start" menu like application which allows one click access to all my portable applications. You should definitely check it out.