Our "Things You Need To Know" document for our heirs has the following topics in it (and of course they'll know where to find it):
Contacts: Business partners, people we routinely do business with: realtor, lawyer, accountants.
Things to do: Add a change of address so mail goes to their home, refresh it at the end of the next 2 years to get those once a year documents.
Where things likely are in the house: Documents, checkbooks, mortgage coupon payment book, gun safe key, keys to rental properties, etc.
Land: List of property and the URL for the registry of deeds to double-check the document is up to date. Associated payment schedules and bills for those properties.
Accounts Receivable: Any mortgage notes or loans that others owe us for.
Liabilities: Mortgage, property taxes, HELOC.
What do to with things they don't want: Suggestions for places to charitably donate the items to and local estate sale companies that do a good job.
Burial wishes: Keep it simple, keep it inexpensive, have a wake and invite our friends.
Family obligations on farmland ownership that's shared with my mom's side of the family: Advice on how to handle things and what we would recommend if other relatives want to sell.
Banks: Banks we do business with and why
Investment Accounts: Places that hold our stock/bond portfolios.
Insurance: Who we have insurance with.
Money and Investment Advice: Little snippets of wisdom that hopefully will help them avoid big mistakes. Plus an attempt to teach the right mindset. Things like if you want a luxury that will require an ongoing expense, set up an investment that will provide an income stream to pay for it.
Hope that helps!