/sci/ - Science & Math

I'll start:

First is hunting by the men and gathering by the women. Possibly an Atlatl or spears would be nice to develop. With strong wood nearby we might even be able to construct bows.
Next is agriculture, possibly also by the women, depending on how difficult hunting proves to be. (hunting/gathering is important until agriculture really kicks in)
Next, try to re-invent pottery by heating mud or clay.
With clay pots I would develop water filters with sand and rocks and a water boiling station for drinking, bathing, and sanitation.
Next we seek honey and sugar for the development of mead (safe to drink, used for recreation and as a reward mechanism) that'll take several months to develop.
Next we stretch the limits of pottery to try to make large vats in the ground that can be sealed. If successful, we all urinate in one vat and defecate in the other. Hay is added to the urine vat and in a year or so we can extract ammonium nitrate for gunpowder. The defecation vat can be used as a source of fertilizer and methane gas, provided we develop a method of air-tightening containers and a method of methane harvesting.