Gasmasks can be provided, along with reserves of oxygen lasting 1hr piece. There is some 20 pieces of oxygen bottles.
Flashlight as well
as for the chalk, you could probably use some of smaller rocks from the ruin, but instead, you might prefer RFID tags with display. The same type as the ones used by the previous team (they glow in darkness), showing timestamp of placement, and are having signal 1 which means they can be wirelessly spotted from 30 meters. You can take 50 of those with yourself. Batteries in each of them last for about a year after placement. .