I think you need to break it down a little more than TSHTF. How about these categories just so people can get a handle on what challenges the folks in our scenario will be facing.
1) Environmental catastrophe. Yellowstone supervolcano, dinosaur killer meteorite, pole shift, giant firebreathing lizard, etc.
2) Societal upheaval. Revolution, riots, pandemic civil unrest.
3) Plague. Rapid moving widespread disease.
In all 3 scenarios essential services will be swamped. Backup is probably not coming, at least not soon. Expect the infrastructure to fail quickly. Electricity, water, line gas, maybe even sewer service will be available only at the onset of trouble.
But as long as we're in tinfoil hat land we may as well have some fun with it.
If you have the resources you have already identified a location for a vacation home that will be outside the trouble zone and will keep you safe enough until the trouble passes. You've seen the warning signs and you've gotten the heck out of Dodge. If so, we can ignore you, you're already safer than the folks in their primary residence in the suburbs or the city. If you didn't get out of town ahead of time or you aren't rolling in dough, then you are left with making your little pink house into a fortress. Just like the rest of us.
Make Shutters: A sheet of 3/4 inch plywood cut to size over ground level doors and windows. Reinforce on the outside with a 2x4 nailed or screwed through the plywood into the lumber. Two 2x4's on a window, three on a door. Drill at least two holes through each 2x4 and plywood for long carriage bolts. Put the shutter over the door or window opening and thread the carriage bolts through a 4x4 cut at least a foot wider than the door or window opening. Use washer at both ends and a nut on the inside to secure the shutter. If you want to get fancy cut small vision blocks and firing ports into shutters.
Plan your keep In a two story home plan on falling back upstairs. Don't select a basement, even if there is a second means of egress. You have to fight your way up to the level where the BGs are from a basement. From a second story you have the advantage of height and even something as simple as heavy items become weapons. An attic with a ceiling hatch will work almost as well if you have a stepladder that can be pulled up behind you if you need to fall back.
Get the things you will need to survive where you will need them. Food, water, clothing, medical supplies.
Get upstairs and destroy the stairs. replace them with a ladder that can be pulled up once you have fallen back. This simple tactic can foil the BGs plan of forcing entry and getting to what you have.
Make sure you have things to keep you entertained. Since the power will probably be off plan on reading a lot.
Limit cooking. I believe the estimate is for 5 days of food in stock in the average American city at any given time. After that people are going to come scrounging for food. The smell of a hot meal will bring them running like rats.
Discipline your light use. Improvise light curtains. Use lanterns sparingly and preferrably in an interior room with a well curtained window.
Plan on what you will do if the sewer fails. Since most sewer systems operate on gravity they will be the last service to fail. However, heavy rains and lack of operators can lead to failure and you should have a plan on how to deal with human waste. A trash bag and a cardboard box may be unpleasant but it beats living in your own waste.
Plan your escape route A window that opens onto a roof or a hatch cut through the decking are good ways to get out of your second story redoubt. Make sure you have a way down to ground level on the roof. A rope or a ladder secured to the shingles is a good idea. Prepare a bailout bundle. A backpack loaded with the basics for two days and a weapon should be on your egress path for you to pick up.
Finally, fire will be your biggest worry. Either because the BGs are trying to burn you out or because of spreading fire. Without a modern fire department your chances of controlling a house fire are about nil. Modern houses are filled with so much plastic and man made materials that they are essentially refineries in a dry state. Hold what you've got for as long as you can, but plan on having to run hard and fast if TSHTF.