Aruch HaShulchan, Laws of Tzedakah, 251:7

Afterwards they brought the words of the Gaon and this is a different matter altogether; regarding one who does not have a lot, and only has enough to satisfy their basic needs - a little bread and water - then that person’s life comes first (before anyone else’s). And they cite the gemara that describes two people traveling, who have nothing save for a jug of water that is not sufficient for them both (Baba Metzia 62a), in which case, the owner of the water [drinks the water] because her life takes precedence. And accordingly, he also cites the case of the widow of Tzarfatit that was similar (Kings I, 17:12). Therefore, if there is extra bread, one first supports their parents, then adult children, and then their siblings, etc. Therefore, what we have cited from Tana D’bei Eliyahu, the intent there is similar, and it says there that if there is extra bread, one party precedes another. And it also says that if one has food in their house and requests to make it tzedakah; meaning, one has just enough food to sustain one’s soul, and is legally exempt (from giving tzedakah), if that person wants to lessen their share of food, they should first give to their parents, etc. [Translation by AJWS]