The first consumer items custom made by default will probably be handbags. They'd have the highest value proposition for custom manufacturing. Hair accessories would be easier, but not as worthwhile, and clothes would be very worthwhile but not as easy. But I've been dragged along handbag shopping with women, and there is always some very specific set of properties they are looking for, all individual to the woman in question. One wants a big, deep bag with a short strap and a wide opening, while another wants dozens of tiny pockets stitched together and several openings. I am certain, with a few very basic mix-and-match components, you could make handbags to order quickly and easily, though perhaps not very cheaply. But if they're made of good materials, people will pay for quality.
Mokalus of Borg
PS - That's the theoretical business model, anyway.
PPS - And likely to stay theoretical.