Just on the surface of it, it looks like collection of goods when they are abundant is not illegal, and really not likely to be seized. What appears to be called 'hoarding' is really 'scalping', selling goods at inflated prices.
When someone goes to a disaster area and sells water, a basic human necessity, for $10 a gallon, that's scalping. It's making a large profit from a survival situation.
To respond to the original question of this thread, a BOB is a portable container of goods for an emergency, designed to save your life or make it easier to survive until you can get to a certain place. It's not intended as a long-term collection of goods.
If you have to run away from home (or sometimes, you're just trying to get home from somewhere else), you take the necessities so you can survive the chlorine leak from an overturned tanker or something, or a threat that doesn't materialize. As soon as possible, you want to go back to your large supply of goods, as long as they are still available (not burnt up, covered with mud or water, etc). Even if your house collapsed during an earthquake, much of the stuff you had stored is still probably there, so you just have to work your way to it.
You do the best you can with what you have.
Sue