Almost anything can be purchased if you have the money. Of course it helps to be wealthy, or a member of the political class, military elite, etc. Just look at the poorest countries in the world where the store shelves are bare, but the elite have access to anything they want.

Having said that, I doubt there will ever be shortages of core staples like beans, rice, wheat, olive oil, sugar, eggs, etc. Sure, the prices of certain foods may go up, and you may have to eat chicken instead of prime rib for example. But that just means you have to be creative.

To offset actual long-term shortages, homesteading or joining a local farming co-op are the only things I can think of.