4 Tips on How to Identify Food Grade Buckets - wikiHow
One of the benefits of writing a book is that you learn a great deal as you do the research. Food storage is a survival topic that I am still learning about. Found this interesting article this morning about how to tell the difference between a regular bucket and a food grade bucket.
The danger of using a regular bucket for long-term food storage is that chemicals used in the manufacturing process may leach out into your food, which doesn't sound good.
If you are improvising after the zombie apocalypse, I don't suppose it will make too big of difference, as you'll be going through the food fast enough that chemicals won't have much of a chance to get into the food. That's just a guess, based on no scientific data.