I usually have a bunch of head canon ideas about the various franchises I like. I never use them as facts obviously, that would be ridiculous. But, for example, there are several star Trek books (from back before they started going together) that I count in my head as being in canon with the show. Same for Star Wars, etc. Generally, if I'm experiencing a story from a franchise that isn't part of its normal canon work (like books/games for a TV show) if I like the story and it doesn't interfere with the main continuity, I consider it canon. Sometimes, in rare cases for myself I'll ignore a canon story if it interferes with another story I really like ( I completely ignore the stupid "mandalorian" episodes of SW: The Clone wars, for example). The Star Wars EU had a great canon system, with various levels of continuity. In general I'm a fan of canon and continuity.