Never buy plastic/paper/whatever bags in supermarkets. Bring yours and if you forgot them for whatever reason, lurk for trailing cardboard boxes. Supermarket are often filled with those. They are solids and the supermarket is going to thrash so they don't care.
Same when you move out, don't buy boxes. Go to your local library to ask them to put aside some cardboard boxes for you. Books cardboard boxes are really solid and always clean. When you are there you can also buy Mutual Aid: A Factor of Evolution by Kropotkin.
Some years ago I accidentally took home one of those plastic shopping baskets from Kroger. I take it in with me on my trips to the grocery when I don't need more than a basket full. They have long since changed models and color of basket, so it doesn't really look suspicious. Someday, maybe I'll have my own cart too.