What rational human beings use on their bread and other bags: bread clips.

A bread clip' is a device used to hold plastic bags (such as the ones sliced bread is commonly packaged in) closed. They are also commonly called bread tags, bread tabs, bread ties, bread crimps, bread-bag clips, bread clamps, or bread climps [1]. By sealing a bag more securely than tying or folding over its open end, the clip or tie may preserve its contents longer. In some cases, the color of the tag indicates the day on which it was baked.

There are two different types of bread clips—the common one-piece plastic clip, and a more complex mechanical clip. One particular design of bread clip is the subject of a patent[2] in the USA.