There are programs that require no more than to be unzipped, can be used on multiple computers, don't write to the registry, and fit neatly on your flash drive. These are called portable programs and there are hundreds out there. I'm going to give you the ten you won't be able to live without.
OpenOffice.org
OpenOffice.org is one of the most well-known competitors to the Microsoft Office suite. OpenOffice comes with a word processor, spreadsheet program, database program, and even a math and a drawing program, all at a great price: free! The program even reads Microsoft Word documents, including that pesky .docx format, and the setup is similar to Microsoft Office, meaning an easier transition to OpenOffice. In fact, OpenOffice was one of the first portable applications I ever used.
Firefox Portable 3.0.14
Firefox is another alternative to a widely-used Microsoft product: Internet Explorer. Firefox is a free, open-source web browser made by Mozilla, the same people that brought you the Thunderbird mail client. What makes Firefox such a great tool isn't the fact that it does everything Internet Explorer does but the thousands of extensions that do everything from downloading torrent files to finding good SEO keywords. Just like OpenOffice, Firefox Portable does everything fully-installed Firefox does except it can be taken with you on your jump drive. Neat, huh?
ClamWin Portable
If you find yourself downloading suspicious files, the last thing you want is to infect your jump drive that you use on multiple computers which might not belong to you. Enter ClamWin Portable. ClamWin is pretty good antivirus software, and the portable version is no different. ClamWin is a very powerful antivirus engine with high detection rates and regular definition updates. Unfortunately, it lacks an on-access virus scanner, meaning all files will have to be scanned manually, and automatic updates and scheduled scans are not available in the portable version.
InfraRecorder Portable
Windows XP does not have native support for burning DVD. Vista does, but since alot of people don't like Vista, you may be stuck on a Windows XP computer needing to burn a DVD with no way to burn one...but not anymore! Infrarecorder Portable burns both CDs and DVDs. It can burn data disks, video disks, audio disks, disk images, and even bootable cds. The full version comes with an audio CD ripper, but due to copyright infringement issues, must be downloaded from the site.
WinRAR Unplugged
The .rar format is one of the most popular compression formats available, and I, for one, can't live without WinRAR, which became a problem when I needed to unzip .rar files on other computers. Luckily, I came across WinRAR Unplugged, the portable version of WinRAR which supports not only .rar but .7z, .zip, .gz, and more! It supports password-protected files and broken up archives (files with that pesky .001, .002, etc. extension). WinRAR Unplugged is not free, but there is a trial version available.