Store magret duck breasts in your freezer, then thaw before cooking.
Magret duck breasts are usualy cooked (often roasted) after first having much of their fat rendered off. Rendering the fat not only crisps the skin, it also imparts more flavor and moisture to the meat.
See How to Render Duck Fat for instructions. You will end up with a lot more duck fat then you need to cook the breasts, and rendered duck fat is highly prized as a cooking fat - use it to saute ingredients as you would butter or oil.
Duck breasts are very versatile, pairing well with a wide variety of other flavors. Ingredients often used with duck include apples, ginger, Szechuan peppercorns, lemon juice, soy sauce, wild mushrooms, oranges, rich & fruity red wines, green onions, spicy chilies, honey, cilantro, star anise, thyme and berries. It can be served sweet, savory, tangy, smoked or spicy.