Stock what you eat. Eat what you stock and put it in rotation.
Get a pressure canner, jars and lots of lids. Be prepared to not have refrigeration or a freezer.
A good dehydratior like a American Harvest Garden Master will come in handy. So will a vacuum sealer.
Get a good water filter (Berky recommended), some calcium hypoclorite to treat water. We just put solar backup in for our well.
Heirloom garden seeds, gardening handtools even some chickens will help keep you fed. A hog or three even more so.
I smoke my own hams and bacon.
Look for stuff on craigslist or freecycle or your local flea markets.
We have reduced our food bills and prepped using these methods. If we go dark the only thing I will miss is ice cubes and internet.
The most important thing is “Don’t panic!”.
And don’t forget spices and herb seeds.