Imagine 100 years in the future and one of your descendants wants to know about you. First, starting at the beginning of your life with a copy of your birth certificate. If you don't already have a an original certified copy, it's good to order one anyway in case you need it for something. They can be ordered for a few dollars from the city or state Dept. of Health (it may be an agency of a different name...just go to your state's homepage and search for "birth certificate"). I recommend ordering 2 copies and storing them in different locations.
I also made a copy of my high school and college diplomas and my CPA certificate. If you travel a lot, put your expired passports in the file. A copy of your marriage certificate, wedding invitation, wedding menu, should also go in the file. Divorce records too if you want that information to be known (maybe not the financial stuff). Some things that may be hurtful now can actually add some spice to the family story for future generations. My gg-grandparents Abram & Sarah Klein were divorced in NYC in 1931. Sarah is always referred to as a "whore" (along with her sisters) when I mention her name to my aunts. I don't know about her sexual activities after the divorce, although later in life she was living with a man, an old friend, without being married. As it turns out though, it was Abram who couldn't keep his pants buttoned. Sarah divorced him for cheating on her. I was able to obtain a copy of the divorce papers which read like a Yiddish spy novel. She sent two friends to catch Abram in the act in an apartment near his Coney Island butcher shop. Their testimony is in the divorce records. I know it's a serious subject, especially since her oldest sons were already out on their own and she might have to survive on her own during the Great Depression but maybe it shows that Sarah got a bad rap. I've heard that she wasn't a very pleasant person so she may have had to make ends meet however she could.