I have been meaning to write out a list... good question.
Find a way to keep and maintain a good clean source of water...
Learn about native plants and herbs to your environment; cultivate and harvest your own, including herbs.
Keep plenty of mined Sea Salt
on hand for Sole, etc.
Keep plenty of a good clean Kelp on hand along with some iodine, H2O2, learn to make Colloidal Silver
, Sodium bicarbonate, potassium bicarbonate or carbonate, calcium carbonate and/or calcium hydroxide, magnesium citrate (if you want another form other than Epsom Salts
Most all of this stuff should remain available as it is used for livestock, food, wine and beer making, gardening etc. etc.
About the only vitamin that may be needed is C... and ascorbic and/or citric acid
should remain available for food and beverage uses as well.
This is with the idea that good non-processed raw foods (this seems to be threatened as well), including fats and oils will still be available like olive and coconut oils etc.
Also, source EVERYTHING you can locally and be as self sufficient as possible growing your own food etc.
Hopefully others will add easily sourced non-threatened sources of nutrition and we can get a real good list going.