Store More Weapons
It is possible to store more weapons than you have space for. First, at the mission prep screen, fill your inventory with the weapons you want to store. Then, fill up all of the available room in your vehicle with items. Equip a survivor with the weapon you want to store, and then switch their weapon to the one they started with. The unequipped weapon will be stored in the vehicle.
Finding All the Collectibles
You will need to play through the game a second time to find all of the collectibles.
Selecting Different Game Paths
At certain points, you will need to choose between two locations when you're in a vehicle. Once you choose one, you won't be able to visit the other in the same play-through. To visit them all in two play-throughs, choose all of the locations on one side during your first play through, and choose all of the locations on the other side during your second.
Keep Survivors Safe
Keep survivors safe and finish the campaign with them in your party in order to rescue them. The best way to do this is to get the vehicle keys and leave survivors in the vehicles during missions. You will need to play through the game a second time to rescue all of the survivors.
Saving Vehicle Keys
You can use four vehicles in the game. The game does not save your vehicle keys until you reach a checkpoint, so if you find a key and then die before the checkpoint, you will need to find it again.