It's not an equivalent comparison. Very few people need bottled water. They could bring a thermos of water, but they don't. There are a lot of similar products that are still purchased often by the masses.
Most grocery store products are packaged in single use plastics. Cereals are sealed in a plastic bag. Meats are wrapped in plastic packaging. Milk is sold in plastic bottles. Yoghurt, bread, baking powder, pasta, medicine. Its not feasible to avoid by choice.