I also purchase bolts from *BattMart* . also when connecting threads has their batting sales I pick up a variety of sizes, generally the ones smaller than my bolt is wide, throws, baby size, craft size, queen & king wool and a couple queen black battings so I have a good variety of sizes, types for what ever comes along.
I also piece scraps and use them up. I just butt the edges together and zigzag them together. Often the cut away pieces are perfect for throws, kid/ baby quilts or for raggy quilts