Portable versions of web browsers for your USB. Good to use at school if they don’t have updated versions 
Also don’t forget this Firefox plugin called “Web Developer toolbar”
This allows you do disable CSS and images also you can check your code with unbuilt WC3 for CSS etc.. good for debugging problems.
Web Developer Toolbar for firefox/flock
https://addons.mozilla.org/en-US/firefox/addon/60
Firefox for your USB.
http://portableapps.com/apps/internet/firefox_portable
Opera for your USB.
http://opera-usb.com/
Flock for your USB.
http://blog.itdunn.com/pocketflock/
A heap of programs available for USB devices to install on them.
http://portableapps.com/apps