Oh yes! I save boxes. You never know when you'll need one. Before I retired, I got several boxes that reams of paper come in. Now I have no source of those wonderful, strong boxes so my 'stash' of them is dwindling, but I still have a few.
I use the plastic bags in the small trash cans for trash and garbage and I have a supply (another stash) of them saved up.
I have a supply of those large 'kitchen size' bags, too. I got bunches of them when I volunteered at the thrift shop. People donated stuff in them and the volunteers would toss them when they emptied them. What a waste! So I rescued them. Recycling at its best!!
Except for plastic bags for food, I haven't bought plastic bags for many years.