Line a cardboard box with sheets of polystyrene foam to help insulate it. Use duct tape to hold the polystyrene foam in place.
Put a trash bag inside the cardboard box. Fold the top of the trash bag down over the top edge of the box and tape it to the box so there are no seams or openings.
Line the inside of the box with aluminum foil to increase its insulating properties. Cover the top, bottom and sides. Place it right over the trash bag and tape the aluminum foil down with duct tape.
Cover the lid of the box with a trash bag and aluminum foil. Use the tape to pull both taut, so the lid fits snugly on the box.
Fill the box with ice or cold packs and put your food and drinks inside. Leave the lid on the box as mush as possible to keep the items cold.