If you are looking for a portable wiki that you can easily carry around on USB stick, look no further than Tiddly BackPack. The entire wiki software is contained inside a single HTML file and requires no installation - just download the file, open it in any web browser and start creating your wiki pages.
All edits made to the wiki are automatically saved in the same local HTML file that you can be easily moved across computer or you can send the full wiki to someone else via email. There are no databases or external files to worry about.
When you run the portable Wiki for the first time, the browser will show a security warning - just remember to grant permission for local access and you are good to go.
You may use Tiddly BackPack wiki for creating notes, managing TODO lists and even for GTD. I guess the wiki should also work on mobile phone browsers. It requires no tech knowledge but if you know some CSS, you can even customize the layout of the wiki.