Zip lock bags are used all the time. Food grade and fine up to certain temps. Pretty sure any temps you might want to use,though you can google it to confirm. There's a lot of BS out there. Some claim using a cooler might be bad because they worry plastics in a cooler can leach stuff into the water. BS-you're not exposing the food to water...just the vacuum sealed bags the food is in.That said, I invested in a vacuum sealer. Bags you can buy cheaply on amazon. If you use ziplock bags, you're using the, "water displacement method". Works as long as you get a complete seal. Once-in-a-while you may not get a good seal. If that happens, water or air gets in and your food gets ruined. If you do go this route, go with freezer bags, not regular ones. Made better. Try to leave enough space at the top so you can clip the zipped part above the waterline, yet still have all your food submerged. Hope this helps.