Empty flask

Oil needs something to be carried in, and this is it. The tallow melts into it inside the bag, and once the oil is poured into the lamp the flask comes back empty, so the same few flasks go on being filled all the way down: what you spend is the fat, what you keep is the glass. If the bag has no room for it when it comes back, it is left on the ground at your feet and the line says so, because a flask gone without a word is a flask you then go looking for.

They are few on purpose: three in the wood and two in each of the four chapters after it, the first always a few steps from a cake of tallow. The note over one found on the ground says that whoever emptied it came this way before you, and the light it held was not enough for them. The brazier at the end of the third chapter takes its oil the same way, and gives the flask back.