I think of it whenever one of these things stir my memory. Like when I am searching the music on my iTunes library I'm reminded of who these bands came from, which person from my past or present told me "Hey, you should listen to this. I think you would like it." There are even some bands that I didn't like when I was knew the person, but who I like now or they double up where one person got me to casually listen to a band but another person got me really into it.
For awhile I just thought of this in terms of music but the same can be said for television, movies, and books. One of my favorite movies Hot Fuzz I saw the premiere with someone I dated who I haven't heard from in years and it just so happens that it's one of my closest friend's favorite movie as well. Game of Thrones will forever be linked to this group of friends I have now even though the future of that group watching it together may not be certain.
With books this concept bears much more weight, being an avid reader. There are books and authors forever linked to people who I've either had long discussions about, read with at the same time, or either recommended or had recommended to me. One friend is linked just to the process of buying the books. I would pick her up from her house, drive to the nearest Barnes & Noble, buy a ridiculous amount of books, then go grab something for dinner. That experience will be linked to certain books every time I look at them.
There are people in my past who I no longer speak to or think fondly of but will be reminded of them in a positive way by the impressions they had on my taste. I guess this is why I sometimes see on a musician's or author's webpage comment section you'll see comments like "Your creative-thing-you-made got me through a hard time in my life" even when that said creative-thing-they-made is not linked to whatever problem they had whatsoever. It's just a thought.