i'll just add that in addition to a will or trust one of the kindest documents a person can leave whomever is left to deal with their final affairs is a listing of information that includes (but is not limited to) the following-
names of utility companies w/phone number (including whose name the account is under/account number)-it's hard enough to cancel service when you're not authorized as a contact on the account, harder still when you find out 'mom' never changed it out of 'dad's' name when he passed 30 years earlier (then you have to find dad's death certificate and paperwork on how any deposits were to have been paid on his death)
names of companies with contracts/phone number/account numbers-things like life alert, cell phones, home warranties...
list of credit cards/account numbers/if established-passwords. much easier to go down a list to call each and determine if there's anything owed vs. having to wade through bank statements (and it's a nightmare if deceased did all on-line payments and go e-statements)
list of life insurance/death benefits potentially eligible to-again, a nightmare to track down without information
list of former addresses, and ideally something that showed the deceased lived there at one time-mom passed 4 years ago and there's still a small amount of money on one state assessor's unclaimed property site but we will never be able to get it b/c we can't prove she's the named person b/c we have nothing that links her to the decades old address
location of any storage lockers and ideally a spare key-never would have located one except a hospitalization caused non payment of the rent so we found a phone message from the facility on her answering machine
location of last few years of tax returns-it can at least provide a guideline for how the final year's taxes should be completed (esp. if someone has obscure deductions or sources of income).
finally-if you receive or will potently receive a pension, find out what whomever administrates it requires to have on file to report your death/arrange for any eligible survivors to receive on-going benefits/apply for any lump sum payouts or life insurance. this is especially the case if a government employer is involved-we had a nightmare dealing with CalPERS

oh-and it's REALY nice if you can include with the above items notarized copies of your birth certificate, marriage certificate, any predeceased spouse's death certificates b/c if they are needed it can take upwards of months to get them from some counties