I routinely use ziploc bags (the ones without the zipper, which tends to leak) when I intend to eat the dish within a day of SVing. If I'm going to freeze it then I vacuum seal it to prevent freezer burn. I gather that there is concern that heating the polyethylene makes bad things happen. I haven't seen anything authoritative saying that this indeed a real problem and my family seems to be fine. (for perspective, consider that browned crusty meat and smoked meat are chock full of proven carcinogens). Beer coolers are great, but with a powerful immersion heater you might do great using a small pot with a towel for insulation. Worth doing? But of course!