The LDS is an excellent place to buy food for long term storage and one of the cheapest. I have their #10 cans of wheat stored and some other things. Every fall, I also buy a couple of 50 pound bags of wheat from our local MFA (Missouri Farmer's Association) and set the bags into a metal garbage can, to protect from mice and bugs. But be sure to check it for quality. Usually it is clean and good quality, straight out of a combine. However, this year one of my bags looked more like floor sweepings, with lots of dust, dirt, straw and trash.
During the winter, I feed this wheat to the birds; but if need be, I could cook or grind it to eat - I do have a couple of the cheap grinders.
The corn grain that I have purchased from Tractor Supply has been very clean and I would have no problem eating it if food gets scarce. However, remember that this "feed grade corn" is mostly GMO.
I also raise sweet corn and it can be eaten fresh or we can let it dry on the stalk like "feed grade corn". It is not GMO and neither are the other corns that you see in the garden catalogs.