For about the last year I have been building a disaster bag, known by other colorful monikers such as "go bag", "bugout bag", "SHTF bag" or my favorite, the "zombie apocolypse bag." When this bag is done right, what you are preparing for really doesn't matter because the goals for building it are the same. The experts say that this type of bag should have everything you need to survive for 72 hours--everything.
Even in my 4000 cubic inch backpack, space is at a premium, so I've been looking for the most calorie-dense food I could find, and I think I found it. These are a pack of 4 2400 calorie emergency food bars. Boy are they dense. One of the reviews said it was like eating a brick graham cracker and I can believe it. These bars feel like bricks. But hey, I wanted dense, and dense is what I got. Two of these bars went into the disaster bag and the other two went in our vehicles. At about 6 bucks each delivered, it's cheap insurance.
Here's the pack I use. It's a TETON Explorer 4000. This is a photo of when it was new. It's packed to the gills now, and someday soon I'll be posting photos of the bag and all of its contents.