Not strictly portable, but you can enable offline mode in Chrome and copy the Chrome user profile to a USB drive. Then, on any PC with Chrome, you can edit Google Docs without internet.
An Analysis of the Concept, Feasibility, and Risks of Portable Microsoft Office 2013
Disclaimer: Microsoft does not officially release "Portable" versions of Office. Portable versions are modified, unofficial releases. This guide is for educational and archival purposes. It is always recommended to purchase and use official software to ensure security and receive updates. microsoft office 2013 portable
Some "portable" versions are actually a lightweight Windows PE environment with Office 2013 embedded. Booting from USB loads a mini-OS.
Pros: Runs any software, not just Office. Cons: Requires rebooting the host computer; slow; complex. Not strictly portable, but you can enable offline
The bottom line: All these methods are unofficial, unsupported, and legally gray at best—outright illegal at worst.
If no official version exists, what are you actually downloading? Typically, three methods are used by crackers: Some "portable" versions are actually a lightweight Windows
This involves a modified installer that strips out activation checks. The portable launcher temporarily copies files to %TEMP%, applies a crack (like a modified SppExtComObj.exe hook), and runs Office.
Pros: Sometimes faster than virtualization. Cons: Extremely high antivirus detection. Often contains malware.