Buy in lots of tins and make sure you've got a tin opener!!! Seriously, if you're talking about food shortages on a national or international level then I would say try to start growing / producing as much of your own food as possible.
Learn how to enjoy eating bugs, grubs and roots? If the Ozone layer depletes and the sun is cooking on the veges - with no rain - then growing your own garden wouldn't work, - and Hey! - can always do what that old couple in the movie "The book of Eli" did - eat people and call it ham.............
Depressing isn't it?
In the movie - they were looking for shaky hands as evidence of eating human flesh, look up Prion diseases (transmissible spongiform encephalopathies)