1. In a large saucepan, stir together first six ingredients. Add next 4 ingredients (through hot water); stir to combine. Bring to a boil over high heat, stirring frequently until salt and sugar have dissolved. Boil 3 minutes; remove from the heat. Add ice water, and stir to cool mixture. Set aside, and let cool to room temperature.
2. Nest 1 oven bag inside the other to create a double bag (see Note). Place it, mouth open wide and facing up, in a roasting pan.
3. Fold back the top one-third of double bag to make a collar (this helps keep bags open). Place turkey inside; unfold collar of double bag, and pour the brine over bird. Add 2 cups cold water. Draw up the top of the inner bag, squeezing out as much air as possible, and secure it closed with a twist tie. Repeat with outer bag. Turn bags so turkey is breast side down in the roasting pan, and refrigerate at least 12 hours or up to 24 hours. Turn turkey 3 to 4 times while brining.
4. Remove turkey from brine. Discard bags and brine. Rinse turkey under cold water, and pat dry with paper towels. Place turkey back in the roasting pan, and refrigerate, unwrapped, for at least 6 hours or up to overnight. This resting period allows the skin of the turkey to dry a bit so it is crisp when roasted. The turkey is now ready to be roasted.
Note for the cook:
Oven bags (made by Reynolds) are found with other food storage bags at supermarkets. Buy the turkey-size bags. They are food-safe, plus they are big, strong, tear-resistant, and come with twist ties. Do not use plastic garbage bags, as they are not intended for food storage. Doubling up the bags is a precautionary measure against leakage. For the same reason, place the bagged turkey in a roasting pan.