This probably refers to a commercially available plastic bags. Shopping bag is usually used to carry the  groceries from shop to car and from car to home.

Plastic bags are made of plastic, and are most commonly used as carrier bags for groceries and as garbage bags. Plastic bags have all colors and sizes, and with different prints. They are thin, light and flexible. Extensive use of plastic bags spread in the mid-1970s. In 2002, the world was prepared in various sizes and qualities of plastic bags to a total of 4-5 trillion pieces

It is a good question why plastic bags are used. Plastic bags do not decompose and burning them causes toxic fumes. Thrown to the wild and in water Plastic bags cause problems for animals. Also biodegradable plastic bags do exist, but they are not as durable.

The same plastic bag can be used several times before it ends up as garbage bag.  Others prefer to use paper or fabric bags for carrying groceries. In some places, the use of plastic bags has imposed a special tax, or they are banned altogether.

In developing countries, little boys produce empty plastic bags, for example, soccer balls themselves.