Some people think that Windows Registry was not a good idea after all; you will agree if you have a set of "essential tool set" on your usb drive and you have to install the tools wherever you want to use them; things like a PDF viewer; your favorite dictionary; etc.
Experts know that there are some neat utilities out there which do not require any installation and they keep all their settings where they are installed. Some other tools can be made "portable" by tweaking a few settings here and there after installation. One such great collection is Portable Apps and another site, having the mandatory RSS feed, dedicated to the same is The Portable Freeware Collection.
Visit them; not only the idea is nice but you will find some really great tools that should make up your "essential tool set!"