Lists are good. Because I had to deal with UK and Australian probate, bank accounts and pensions, I got an A4 binder with alphabetical inserts.
I put lined paper in, headed up with the name of the bank/utility, etc. and arranged these alphabetically too. I've used them to record the many phone calls I've had to make: date, time, who I spoke to and action to be taken/when. It's been invaluable, still using it.