I've uploaded my script so you can backup your own data. Make sure, your Trakt profile is not private, so the script can access your data.
The data is zipped as JSON in separate text files. If you prefer other formats, you will find converting tools on the web (e.g. CSV).
You can also call this script directly, e.g. save it as a bookmark or use wget:
Although the script doesn't alter anything on Trakt, and I'm not storing any of your data, I have to include a disclaimer:
You can check out the source code on GitHub. Feel free to adjust it and use it on your own web server.