My number one tip, though, is to go through your cupboards and closets and remove those items that are duplicates, that you rarely use, or that you do not use at all. For example, in your kitchen, how may different pots and pans do you need? My guess is that you use the same two or three over and over again. Stow the extras in the basement, attic, or garage, or give them away to charity. Trust me, they will not be missed. The same thing applies to seldom used clothing, shoes and sports equipment.
For global catastrophic risks the costs of food storage become impractical for most of the population  and for some such catastrophes conventional agriculture would not function due to the loss of a large fraction of sunlight (e.g. during nuclear winter or a supervolcano). In such situations, alternative food is necessary, which is converting natural gas and wood fiber to human edible food.
Dust Masks or Respirators- Depending on the crisis, air quality may be severely deteriorated. Prevent the worst of the gunk from entering your lungs by investing in quality fitted N95 or N99 respirators and cartridges or disposable dust masks rated for fine particulate and organic vapors. These are not proper gas masks, as use and selection of protective equipment in preparation for airborne chemical or biological threats is another conversation entirely.
Basic First Aid and Trauma- You cannot count on EMT’s, paramedics, or doctors being able to render aid if you or someone in your group is injured. Take the time to learn CPR, basic wound care, trauma care for major lacerations and penetrating wounds, and how to manage hypo- and hyperthermia. All your nice medical gear you bought up above won’t help you if you cannot employ it correctly and safely.
Just like rice, pasta is a great way to get carbohydrates. I love pasta and I’ve learned to improvise all sorts of meals using it. This is one of the cheapest survival foods you can find and there are many possibilities to stretch a meal using pasta. You can make pasta with tuna, with canned vegetables and I’ve even had pasta fried in lard with pieces of beef jerky seasoned with cayenne pepper. It is really worth stocking up on pasta. Make sure you buy some when you get at the grocery store.
If it’s at all below the level of the water table, it will flood, concrete, steel, or other materials be damned. Sure, there is some top-notch engineering you can do to keep the water out, but it’s expensive. One solution is to put the bunker at ground level and then pile dirt on top of it, but you need very large amount of dirt to protect it from impact.
The Silo Home in Saranac, New York up in Adirondack Mountains makes another incredible underground shelter that will keep you alive when a nuclear bomb hits the big city. The property costs around $750,000 listed on the Saranac real estate. At the site, you will see a regular, cabin-like home serving as a decoy house. However, the real home lies underneath the closet.