I'm not a very nostalgic or sentimental person by nature. I don't tend to get weepy about the past, I have a hard time getting emotional when someone I know passes away, and I rarely keep anything lying around my house that doesn't hold utility in my everyday life.
But there are exceptions. I cry at every movie, TV show or commercial in which a father and son have a real, genuine, emotional moment. I get weepy when my kids say something too cute or loving or precious. I keep old baseball cards, even though they take up space and are largely completely worthless, unless you have a strange fascination with the 1988 Donruss set.