As promised, since October the 8th to the 11th, the bus has been "dropping" several items that may or may not be used for building stuff
Note: The info that I input pertaining to each item is pure speculation.
On October 8th, the bus dropped a car battery with a headlight on top of it at the depot. What I think it could mean is that the bus could run out of electricity at one point in the map and the players have to scavenge around for an extra battery from the other cars. OR the players reach a certain part of the map where the bus is no longer needed and they take out the battery of the bus and use it to turn on the power at the power station and summon the electrical zombies. (Or use it against electrical zombies?)
Another great idea (thanks to an anon) is that this is how we use Perk-a-Cola machines before the power is on.
On October 9th, the bus dropped a ladder at the diner. This could possibly an item which can be picked up (and make the player vulnerable like a player who picks up a sentry) and be moved to other places to reach higher points of the map. It may also can be used for climbing onto the roof of the bus since the one seen in the background of the reveal trailer seemed a little too short.
On October 10th, the bus dropped a dismantled table. The fact that it's dismantled gives way to the possible fact that the legs (or the cinderblock) could be used for other things rather than just the entire thing. Or it could just be where you build stuff when you acquire the necessary materials and blueprints.
A crafting table, if you will.Another possibility could be that it will be used as one of the planks to use as a barricade or battering ram that can be mounted in front of the bus.
On October 11th, the bus made a drop at the depot, an arm. The description, "This should be the capper for this thing!" means that its not entirely useless. The way this can be acquired in-game could possibly be easy (just dismember a zombie) or in an unreasonably hard way (find it somewhere amongst the undead corpses or CUT OFF YOUR OWN ARM) or find it hanging on the power switch. (Picture is of Treyarch HQ's hallways.) The fact that it's clenched into a fist could mean that it was holding something important... like the POWER SWITCH! (Picture is of Treyarch HQ's hallways.)
As it being a capper for "this thing," I honestly have no idea.
On October 11th, the bus dropped a lawnmower. It could possibly be used as the motor for the new Wonder Weapon we saw at the end of the Reveal Trailer or as the motor for the alternative transport the leaked achievements hinted. (Or you can use it to kill crawling zombies while cutting grass.)
On 11th, the bus dropped some meat. I seriously don't know... a lure? A bait? Also note the glowworm thing inside of it. Maybe that could be useful too? A light source made out of glowworms, hell yeah!
Don't Miss the Bus
A video showing how the crafting system works was released. It only shows the "Zombie Shield." Err, disappointing...