for the placemats, 100% cotton is good, use old jeans or wool from a thrift store,two or three layers of jeans is great, just by themselves and frayed edges. old wool coats for an insulation layer on quilted fabrics. a coat could probably get you about 20 potholders. maybe you can find something stained and get it cheaper.
Those microwave bowls too. evenif you just microwave, you need to wash dishes and could use a pot holder or towel.