yes sir. and it looks like you figured it out fine.
Nah, that's the beauty of it. The next game you play, they'll be prepared. Giving them 20 minutes to pack their shit and run means you'll see a much greater variation in their packs, based on personality and what they see as necessesity.
Guns... Only if they bring them, and remember, unless a gun shop is already open, they're bound to be locked with bars on the doors and windows, and the guns themselves packed away. If they're open, remember that other survivors will be looking to get armed, as most people think "i'll do it if it happens"
If you do run with this zompoc game, make sure of this one thing. They're not allowed anything in their bug out bags unless they bring it to the first gaming session. Tell them by sms that a zombie attack is underway to pack their zombie bag and get to your place immediately.
THAT is all they're allowed to start with in their bag.
That's the only way to start a game focusing on the zombie apocalypse. No warning, just BLAM!
If you've anyone in your zombie game who was a scout, or is prepared already for the zompoc, you're going to have an excellent game. Otherwise, it'll be a thriller.
Don't use the Max Brooks stuff, write five or six attributes of the zombies, whether or not they decompose, how fast or slow, intelligence levels, senses and so on... You know how stupid people act in disasters and emergencies. Watch a few disaster movies and extrapolate from that.