Journals, letters, books or gifts to leave for your kids

My Grandfather wrote a book about his life & his parents life for the family, and also kept a diary.  It's interesting to read how things where back when he was a child, and his thoughts on life as it happened.  I read his diary entry for the day I was born and he says "(Mums name) had a baby girl today, what a beauty."  In another part he also talks about helping to build roads in their area.

So I'd say times and ideas will change over time, so put your life & thoughts in writing for them.