Another dream

I dreamt of a zombie apocalypse (I've had many zombie apocalypse dreams) in which I was on the top floor of a sky scraper with other survivors. In the distance, we could see white balloons floating towards us from beyond a layer of fog, and attached to the strings were supplies. We sent our own balloons back the same direction, with notes attached. We continuously received new supplies via these balloons but our mysterious benefactors did not respond to our notes. At one point, they sent books, however, the books fell to the street level. I had to venture outside to retrieve them, risking my life. I remember running from zombies, running into a hut and trying to blockade it. I remember little else.