Not every PC problem your friends have will require a malware scan or an alternative boot. These portable programs easily fit on your flash drive, and can run in Windows without being installed.

: If any type of software should be portable, it's an uneraser, because every time you write to your hard drive, you lower the chance of successfully restoring a lost file. You'll never find a guaranteed file-recovery tool, but in my experience Piriform's Recuva has an amazing track record.

: Here's another excellent, free, and portable tool from Piriform. As the name implies, this one cleans up your friend's messes. It empties caches, cookies, and other Windows and application garbage. It cleans out the Registry (do this with ). It can also uninstall programs, although not as well as my next recommendation.

: Every Windows program comes with an uninstaller, but many of them leave junk behind. Windows' own Uninstaller tool (called either 'Programs and Features' or 'Add or Remove Programs') isn't any better--it just launches the selected program's own uninstaller. Revo, on the other hand, runs the program's uninstaller, and then cleans up the remaining garbage. It isn't perfect, but it does a reasonable job. One warning: Although the free, portable version works in 64-bit versions of Windows, it cannot remove x64 programs.

: You don't need to boot into Linux to check a drive's status. This program will do it in Windows. This version is free only for personal use; professionals will have to shell out $35 for the more-powerful HD Tune Pro. This is not officially a portable program--you have to install it on Windows. But once you do that, you can copy the folder to your flash drive, and use it anywhere.