I wish I had consistently kept journals over the years...and never thrown one away. My history is in bits and pieces, some stashed in files containing handwritten letters, some in notebooks, a little bit in bad poetry and essays.
During some part of my childhood I kept a diary. I have no idea what happened to it. A couple of years ago, three or four letters I had written a friend when I was a high school sophomore were produced by the friend. They were revealing, and a little embarrassing. My handwriting was atrocious, my spelling not much better, and I wrote mostly about boys.
There's a folder containing letters from two wise uncles (my dad's brothers) who wanted to show their moral support during a very rough time in my life, but I don't have copies of the letters I wrote to them.
I have copies of most of the letters I wrote to my mother during the two years I lived in the South of France, although I think they read more like a travelogue than a journal.
There are two notebooks containing my feeble attempts at keeping morning pages, the primary activity I took away from Julia Cameron's The Artist's Way. The notebooks are not even close to being filled. I think I have an aversion to writing about my feelings.
There's one notebook where I kept notes on my trip to Norway and a driving trip my husband and I took through several countries in Europe. Some of those entries are entertaining, but not terribly introspective.
And the poetry and essays? Most of those have a date with the shredder.
If you don't keep journals now, I recommend you begin. Someday you'll be my age and wish you had a better grasp of your own history and what you were thinking back when. It's surprising how much we forget along the way.