Due to changes to the YouTube website, this script is now obsolete. An updated version is availaible here
To generate an OPML file containing RSS feeds of your YouTube subscriptions:
Navigate to https://www.youtube.com/feed/channels, and scroll the page to make sure links to every channel are loaded.Run the script or activate the bookmarklet. An OPML file will download, and a list of RSS feeds will be logged to the console if you need it.
Works in Chrome, Firefox and Safari as of May 2023.
Related: a bookmarklet to get the RSS feed directly from a Youtube page:
Tested with Firefox ESR (v78)
Source: https://codereview.stackexchange.com/questions/160594/bookmarklet-to-go-to-youtube-channel-rss-feed#answer-160650