Life as We Knew It (Last Survivors #1) - Susan Beth Pfeffer 4.5 Stars.
http://divainpyjamas.blogspot.com.au/2013/07/life-as-we-know-it-by-susan-beth-pfeffer.html
The concept is terrifying. A natural and reoccurring phenomenon such as an asteroid hitting the moon is enough to bring the world to it's knees. The story of death, courage and survival is told from the pages of Miranda's journal, from the few days prior, to the asteroid knocking the moon off orbit, to the horrifying and deadly hell that unleashed over our dying planet. You'll feel every high and low that'll make you appreciate what you have now.

And don't be surprised if next shopping trip, you include a few more non perishable cans to stockpile.

It's simplistic, frightening and unbelievably good.