When I was making my Master To Do List I started with those maintenance jobs like having the roof cleaned. I want to have a list of who I've used before and their phone numbers and what it cost last time. Also places I call for repairs like a plumber. So I'm going to get together than information and add a page to my housekeeping book for it. This list could be used for other things but for me personally this is the information I think would be useful. I have another address book for personal phone numbers.
I could also add phone numbers for the telephone company and other utilities along with my account number. I always have to dig for an old bill to find this information.
Being this list is for house related items my insurance company would be another good one to add.
Another list that might be useful is web addresses of places I order from. I keep them on my laptop, but in case I ever lost the info. it would be nice to have it somewhere else.