Have you ever known anyone with a hoarding problem? Hoarders often collect massive amounts of food and other items.
No, I don't know anyone like that!  What do they do with the stuff that they hoard?
Some hoarders believe that they will be hit by a natural disaster or civil unrest will cause essential items to be in short supply. 
That's a good reason, I guess.  Isn't there a tv show about hoarders?  I think I noticed it one day when looking for something to watch.
Yes! It's called Hoarders on A&E! The show explains how people begin to feel an extreme emotional attachment to their belongings and it becomes almost impossible for them to throw things away. Even if it's obvious trash.
Is it considered to be some sort of mental illness?  It sounds strange to me - I wouldn't have room to hoard anything!
It is definitely a mental illness. And most hoarders don't have room for their stuff either! There have been cases of hoarders becoming trapped when stacks of items collapse on them. It's a really sad existence.