Given that the main ingredients for gunpowder(Charcoal, Saltpetre, and Sulphur) exist in varying quantities pretty much everywhere, I've been wondering how it wasn't discovered much sooner than the 9th century. I know there are some reasons for that but for the sake of the scenario let's assume that this society was roughly the size indicated by the Motza site in Israel(Roughly around three-thousand people). And was situated near a few hot springs vital for the collection of sulphur. With the surrounding countryside filled with large herding animals and dotted with Bat caves needed to supply the dung and/or guano needed to extract saltpetre. Given a small population and limited technological advancement, and given there's a limited amount of each ingredient to be realistically gathered in the local area, what could such a society make with this gunpowder?
Without metallurgy you will be vastly limited in what you can do. Stone is strong in compression, but weak under tension. A cannon is essentially a gas pressure chamber that puts the walls under tension so it would not work.
Instead may I suggest using it to startle and surprise the enemy. A shallow trench filled with gunpowder placed around the perimeter of the camp could be ignited whenever the enemy attacks; blinding and disorienting them.
For other uses, I suggest looking at the history of Gun Powder in Ancient China, which includes such excitement as fire arrows, explosives, and naval bombs.
you can make bamboo cannon (but it prone to kill the user too and not as strong as metal cannon)
even early fire lance and fire arrow are made of bamboo too and theres plenty of type of it.
early chinese use trebuchet to throw explosive gunpowder contain inside ceramic/clay so for a primitive people, maybe they can make a sling or slingshot version for it or even just throw it barehand like ceramic grenade bellow
here the clay/ceramic bomb
another is clay grenade (this one is from japanese ww1 but the early chinese have similar thing like this)
i think for use in stoneage society they can use it to fish bombing and raiding or defense against raid and even selfdefense against megafauna.
I think the biggest advantage could be in firestarting. You ever try to start a fire by rubbing two sticks together? It sucks. It's tiring, it can take a very long time if you don't have the right tinder, it's impossible without dry wood, and depending on the technique it can be easy to give yourself splinters, which in a pre-antibiotic setting can be lifethreatening. Gunpowder doesn't totally eliminate this problem, but it will reduce it greatly. Gunpowder is pretty much the perfect tinder.
Gunpowder can probably vastly speed up mining and other forms of dealing with rocks. Know how they dealt with hard stone before the advent of modern mining? They heated the rock, then cooled it with water until it cracked and broke, then finished the work with picks.
Gunpowder would be a godsend for this.
In order to build a gunpowder-based engine, you will need advanced metallurgy. So I don't think that would happen in the Stone Age. However, an intuitive and easy-to-use use of gunpowder is to use it as an explosive for large-scale landscaping or to trap large prey (such as mamouth).
Very little impact, because gunpowder cannot be eaten.
Lots of questions about technological twists/advances in the stone age fail to appreciate just how undeveloped stone age man was. Never mind the lack of metallurgy for making guns: stone age man could not have survived in one place long enough to gather together the materials to make a useful quantity of gunpowder, because prior to the development of farming and animal husbandry humans were nomadic hunter-gatherers. Time spent chopping down trees for charcoal, collecting sulphur or mining potash is time not spent feeding themselves, and even assuming some group dynamics with some humans hunting while others worked the gunpowder, they would quickly exceed the carrying capacity of the local area. Even having made the gunpowder, they have only rudimentary leatherworking or pottery skills to make containers with which to store it, and it's complete dead weight for as long as they do carry it.
The best thing to do would probably bei to use the black powder for mining flint. In warfare it could see use limited use in clay grenades, but I would Claim, that Stone Age armies are too scattered for it to be effective.