@pepper I think the best way to find feeds is to use an extension like Want My RSS for Firefox: addons.mozilla.org/en-US/firefox/addon/want-my-rss/
It adds an indicator to the address bar which lists all available feeds and lets you view them in the browser directly.
YouTube, for instance, exposes an RSS feed for each channel so I can essentially subscribe to them without having to use an account or even open YouTube at all. As for Twitch, it doesn't provide RSS feeds itself, but you can use twitchrss.appspot.com