What if we had a wig-making skill?
I'm not quite sure where it would fit into the tree, probably something in one of the clothing trees. But, my idea is basically, give us access to a group of items that are worn on the hat slot. That changes our hairstyle. I'm not sure how you'd work that for hats to sit atop the hair items, but then I'm not quite sure how the code exactly works for this game anyway. It'd give us, maybe, a secondary use for scalps, and the ability to pluck hairs from animal skins.
Another idea I had, was perhaps, dye-working. Using berries, and such to create dyes for clothing. It'd fit into the sewing/clothing-making tree, and I'm actually surprised it wasn't already included in the game. It'd fit with the wig-making skill, because then we could dye the wigs whatever color. I'd limit the amount of colors people would have ready access too, though. Prevent a lot of neon green, and purple-haired characters from existing.