In a way, I've created time capsules pretty often, without really setting out to do so. Take for example the contents of a shoe box I put together in the 6th grade. I remember collecting the items that seemed important to me at the time; items that I wanted to keep for the future. In doing so, I created a time capsule that says a lot about my 12 year old self.
Inside the box: a 6th grade Olympics/Field Day shirt, a program from a play with did in 5th grade art class, the last Calvin and Hobbs comic, a post card from my mom's trip to Puerto Rico, a map of Six Flags, a luggage tag from a 5th grade class trip, a card from a 4-H project, Christmas gift pencils from my 5th grade teacher, two keychains, a ticket and earplugs from the drag races.
Over the years I've made scrapbooks, many of which contained not just photos, but also mementos. Those are a form of time capsules as well.
At the beginning of the year, I created a "2013 Memory Jar" and have been putting mementos inside all year. I have ticket stubs, a concert pass, buttons, paint chips, note cards, 5K bibs, and more. If I did something fun or memorable, I put something in the jar.
I make these time capsules for myself and doubt that anyone else will be interested in them. It's just fun to be able to look back at my life and have a reminder of what was important to me at a specific time.