There may be no source for raw materials and I cannot see myself weaving cotton into cloth. I like to take a pair of jeans and cut them down into their elements for future use. Jeans may wear or tear at the pressure points like the knees. When a hole happens and the jeans have been mended beyond being mended again, they still leave several useful areas to work with. The patch pockets on the back are good to save.
You can also cut off the jeans at the hips and add fabric to make a skirt.
You can keep patches or strips of real tree camo for making a ghillie suit or a hunting blind.
I like to start with the 'easy s' first. I like people to feel they have accomplished something truly cool when they see their final product. I cannot assume everyone is stocking up on fabric for TEOTWAWKI. Just me, so far. You may have to think about saving what you have to make more from it later. So, if you have no fabric stock, look at your clothes closely.
I give clothes to charity if they are still good and useable, free from stains and tears. If they are flawed, I cut them into scraps fro use later. I have half a quilt in a shoebox waiting for two more pairs of jeans to die!