CLICK THIS BEAGLE if you're looking for in-depth gameplay video run-throughs! :)
If the deck runs out, form a new deck by flipping over the discard pile (no need to shuffle). It's not very common to run out of cards, though - are you drawing cards to reroll black symbols very often?
We've played 7 times now, haven't run out yet, but in one game, we were down to 3 cards left when we lost, so if we hadn't run out of time, we would have run out of cards pretty soon.
Yeah, we're using the card thing to unlock quite a bit... when we're separated, and there's no zombies near the church, it seems like a save bet, because you've got a decent chance that you'll draw a card that won't hurt you too badly