I use the Rival mix. Add about 3/4 cup to each quart bag. Then put in another quart bag before putting in the gallon bag. Wrap newspaper around the bags. I make this with my kiddos at school, and they love it! You have to shake, or you will only have a delicious milkshake. I also use freezer bags since they're stronger.
My high school son made this in his chemistry class yesterday (half and half) and loved it! He just whipped up a batch tonight (using whole milk)and was so proud of himself. He said he really couldn't tell a difference between the two. This is the first thing he's ever "cooked" and hopefully will inspire him in the future. Roxygirl