The week between the holidays and the new year is uniquely useless for anything ambitious and uniquely good for administrative housekeeping. Nobody expects anything from you and every institution is closed.
The subscription pass
Go through a full year of statements and list every recurring charge. Not to feel bad about them — to find the three that renewed at a higher price, the two nobody has used since March, and the one that is being paid twice. This alone typically covers the ninety minutes several times over.
The renewal calendar
Insurance, registrations, memberships, passports, professional licenses. Write down what renews and when, with a reminder ahead of each — early enough to shop around rather than the day it auto-renews.
And what actually happened this year
What was repaired or replaced, what it cost, who did it. This is the record that is genuinely hard to reconstruct later and genuinely valuable when you sell the house, make a claim, or try to decide whether the fifteen-year-old furnace is worth another repair.