Candy bars are well known to supply large amounts of energy for metabolism. With all this energy trapped inside, how can the candy bar sit still on the shelf in the grocery store

Energy is stored as potential energy

Explanation:

Candy bars are primarily made of glucose (and other types of sugars), which contain many covalent bonds that store potential energy. The reason why a candy bar can sit still on the shelf is because covalent bonds are very stable. However, when you eat the candy bar, your body has enzymes that can metabolize the candy, breaking down the covalent bonds and releasing all that "trapped" energy inside.