I lost my DH -- am remarried. All of the advice above is excellent!!! Knowing where everything is (bills, tax info, etc) important. I knew and yet, during that horrible time after, I had problems remembering and filling out paperwork. I can't imagine where I'd be if I'd not known anything!
This is a good idea for everyone - no matter what your health is, no matter how old you are. You never know when you'll be called home.