A general rule of thumb on what items you should put in the safe deposit box is: If you can't replace it or if it's really expensive to replace, then it should go in the box. However, here's a more detailed list of items to include.

1. Copy of your last will and testament
2. Deeds, titles and insurance papers for your house, car and other personal property
3. Birth and adoption certificates
4. Marriage and death certificates
5. Custody agreement and divorce decrees
6. Military service records
7. Passports
8. Copy of your health information (vaccinations, hospitalizations)
9. Copy of power-of-attorney forms (if applicable)
10. Social Security cards
11. Contracts and other legal papers
12. A videotape inventory of your household items
13. Valuable heirlooms

Source:  Dave Ramsey