Ensensu

At the risk of adding more on to a, perhaps belabored, point I can add my own 2 cents regarding this subject. Bone needles seem like they'd be hard enough to take a sharp point and durable enough to withstand much use on the pointy end. For the eye, a knife could be competently used to carefully carve one, much like for a wooden needle so possibly not much of a resource expenditure there except time, light, and a fire to keep warm. I'd second the hours long crafting time, as that's what it took me my first time with a wooden needle IRL. Sharpening bone isn't all that hard, you really just need a rock, any reasonably flat rock with a pitted surface will do really. I can see larger in-game animals at least needing more tools to break their bones down to manageable sizes for needles, bear, wolf or deer bones needing hacksaws for instance, but making more than one needle out of the crafting process, or, perhaps, a stronger one, in addition to what's needed to kill and butcher the animal in the first place. Transitioning this into a refillable sewing kit might be tougher, but very doable. Perhaps if some of the existing Ace Mending Kits can come in metal tins and not just in plastic boxes. Line strong enough to hold fish can already be made from cured gut with the aid of a workbench, which seems like a reasonable compromise on work versus reward to refilling a sewing kit. I don't know if these kits should be a longer term project, although I can see the balance aspect of needing the compilation of many different kinds of materials to make something self-contained, durable and protective of its contents. Bullet casings could be cut to work as the sides of thread spools, a credit card sized patch of cured rabbit hide with strips sewn through it could be glued to the inside of the lid to hold multiple needles.