Check out these great SOCK project bags. Each bag is double lines, has a center divider (w/zipper to keep your needles, stitch markers, scissors, etc. in) allowing you to put one cake of yarn on each side... there are even snaps on top to keep your yarn stablized.
All bags are HAND MADE, by Jo, in a variety of fabrics (more coming soon)!
Get Jo Sock On offers a large option as well... (see Large Sock Wrist Bag)