For all the important documents, you would never want to lose them. First and most important thing to do is, of course, not to lose them in the first place. Put them in a safe or some dedicated place where you know you can find them. Also, it is very important to keep a copy of all the important documentations.
When you do lose them, most of the time you don't know how to replace them nor who to contact to get more information. Now not to worry and put the panic aside. The bargaineering.com put to gather How To Replace Destroyed or Lost Important Documents page.
Social Security Card
Title Insurance Policy
Marriage License (and Divorce papers)