If I the zombie infestation had driven me out into the woods, I think my sewing skills would soon improve, from jsut wanting to keep things together and also because I would want something to do to keep my mind busy.

If you want to make clothes, several skills may be needed. One, you will need you cloth, whatever it is, and preparing that is going to take some doing. This could involve, spinning fibers into threads or yarns. It could involve tanning hides, weaving threads, knitting, and probably a number of other things.

However, if one had cloth, then that ratty pants that have passed surviving another day as anything so much as a loin cloth, may have one further use, as a pattern. Years ago, I wanted to make a ball that seemed to be made from fur. In order to make a pattern, I cut the cover off a baseball. I think I could get a pair of pants or a shirt apart and use it in the sme way.