The plastic garbage bags don't work as well because they'll burst as you pull them over your shoulder with any substantial amount of water.
Thats right, been there done that. Good thing my body weight can bring it up, but I do need some wind to do so. Jaime, you remember when I capsized at the seminar? Barely enough wind to help me bring the boat up.
Try one of those righting bag rigs or like Terry said a Pillow case.