I feel nostalgic for a variety of things, but most of the time it's little snatches of time, little memories that come up one at a time. Sometimes I'll hear a song that really takes me back, other times it'll be the look of a movie or even a comic -- comics have always been extremely important in my life.
Sometimes even just the look of a movie, or its firmly-dated cinematography, fashion, hairstyles, and more will take me right back to a certain period of my life. Of course, over the years one builds up the pleasant times and tends to gloss over the less pleasant ones, but it's still nice sometimes to luxuriate in the idea of what can be remembered.
Some films, too, have a special place in my heart. I remember I used to try and make "movie night" special for myself by drawing a movie poster and scheduling a time to start, getting ready, preparing a snack, everything...I'd turn off the lights and just watch the movie, with nothing else to distract me. I did that as late as early high school, and I always used to love those nights. They were so much fun and something to look forward to.
Of course, some things have been affected by negative experiences or bad people I knew, and unfortunately I can't watch some things with the same feeling anymore. But that goes with the territory I guess.