I would use anything that is avalible to me, that being said I use the same for myself and family. I am currently crocheting plastic sacks together for goodness sakes, so that shows you how un-picky I am lol.(In case you wonder they make wonderful mud rugs,mats to sit on outside , reusable grocery totes etc, they last a long,long time.)
I have steared away from many,many charities because they require certian " quality materials" Some do not have the luxury of an abundance of high quality fabric, and some of the posts I have seen before on this subject makes some feel inadequate to give from the heart....Remember it is what is in the heart that counts ....