Slax is distribution created for USB storages, you can download it from www.slax.org . File weights around 200mb and it gives you your OS on the go so every place you are, your OS is with you!

Download it from www.slax.org. You can even preset what modules you want so you are downloading exactly what you need. You have to unpack it on your clean storage formatted for FAT and to make it bootable, you need to go to boot folder and run:
for windows bootinst.bat
for linux bootinst.sh
After restart, our storage should be seen in BIOS and Linux should lunch without any problems. We can choose few versions but default is KDE session. OS will show up after few seconds and you will be ready to work!
OS has a lot of typical tools met in KDE but the main advantage is possibility to launch additional modules on the fly what makes him clean on startup by unnecessary apps. For example, we can download module with Firefox from http://www.homesopen.com/slax6/index.html and put it in “/slax/options”. By GUI or commend “activate” we can choose our Firefox and enjoy our new program!
We can put commonly used apps to “/slax/base” so they will launch on auto start!
Of course we can launch not only applications this way, it can be drivers for your modem and another devices that don’t have support from kernel. There are many different OSes dedicated for USB like Damn Small Linux, Slitaz or Puppy Linux that i didn’t show you because right from beginning they are poor compared to slax. You can see it by size of this distributions even if we notice that Slax run on KDE. It is worth taking a look at Slax KillBill Edition that has Wine, DoxBox and Quemu or minimalistic version of Popcorn Edition with Xfce.