What it's best for: If you're refrigerating something smelly, foil creates a stronger barrier to keep odors in. Just be sure to seal as tightly as possible. Foil is also ideal if you'll be reheating the food in a conventional oven, since it can withstand heat.
Tips for using: It's a good idea to wrap a snug layer of foil around plastic-wrapped foods you plan to freeze (like meat in its unopened packaging), because it keeps out oxygen, which causes freezer burn. Definitely don't use it in the microwave, and never wrap acidic foods, like tomatoes and berries, in foil. The acids react with the aluminum, leaving a harmless but unsightly blue residue.
What it's best for: Acidic foods and other fresh foods, like sandwiches and cut produce.
Tip for using: To keep foods such as apples and avocados from turning brown, press the plastic against any exposed surfaces. And when you're using a dry marinade or spice rub, you can speed up the rate of absorption by snugly wrapping the meat between two sheets of plastic wrap.