A disposable or reusable and reclosable gussetted plastic bag capable of being compactly stored as a food container in freezers, yet capable of standing with an upright spout in a microwave oven for non-spill thawing and cooking of food contained in the bag. The bag is formed of two wing-shaped pouches on either side of the upright spout. The bag preferably has inner and outer skin layers of different heat sealing temperatures so that peripheral sealing is effected only with the inner skin layers, allowing the wing-shaped pouches to be formed out of a gussetted bottom without sealing of the outer skin layers of the gusset walls facing one another. Two pairs of relief seals are located adjacent each gusset joint at both edges of the bag. Each seal is positioned 45.degree. off the gusset joint and preferably has a radius shape. The heat seals are formed by applying heat adjacent each gusset joint with a hot bar or other heat sealing device following formation of the bag.