If you are starting from scratch, remember that you are essentially pushing out the day you die. I know that is harsh but the further out you push that date, the better prepared you will be.
Without air, you die in minutes
Without first aid, you die in an hour
Without shelter, you can die overnight
Without water, you die in 3 to 7 days
Without food, you die in a couple of weeks
Without sanitation, you die in a month or two
Extras include electrical production and fuel production along with other trade items and skills (soap making, candle making, woodworking, etc)
So, I would advise a first few simple purchases:
Masks - start with basic flu cover masks, later upgrade to actual gas masks (about $250 to $300 per) with extra filters.
First aid kit and know how to use it and a supply of gloves and masks, bandages, tampons (the kind you can shove into bullet holes), medications, and a good first aid book. Hydrogen peroxide tends to go bad over time so I like iodine and bleach for sterilization.
A supply of water that can be obtained without power. This will likely mean you will need to filter and purify on your own. A small personal hand water pump filter types might be enough if you have one per person plus some extra filters but I prefer to also have larger, higher volume gravity fed filters. Large clear glass gallon jugs can be used to take the filtered water into the sun for 8 hrs to kill of most of the critters in the water.
Guns and ammo and the skill and will to use them to defend yourself. At a minimum, a handgun, a shotgun and a rifle. Preferably one of each per adult. Reloading supplies with the correct dies and bullet casting extends this even further. Minimum 100 rounds each weapon that is your stock (different from training ammo) but 500 per is better.
Shelter that is able to sustain you against first the cold, then the elements, then the sun, and finally, the externals that WILL attack. Remember that stick built homes offer ZERO bullet protection. Concrete, brick, sandbags, etc are needed to provide a barrier.
A transit food supply (prepped food) and a long term food production (garden, greenhouse, etc)
After that, you can start to work on the extras:
Power production (off grid solutions)
Fuel production (ethanol or bio-diesel)
Supplies for trading items (soap, lanterns, ammunition, gold and sliver, lighters, propane, etc)
Supplies for trading skills (first aid items, wood working, welding, etc - what ever skills you have)
So I want 500 rounds per weapon/caliber? What do you expect me to do the all the extra?
>>Hydrogen peroxide tends to go bad over time<<
Where in the Sam Hell did you ever hear that crazy idea? Hydrogen peroxide weakens once the contents are exposed to the air. It does not go bad. So, store it in small bottles and only open one at a time.
http://www.drinkh2o2.com/#hydrogen-peroxide-safety-storage