Final answer:
A gallon of milk used for cereal is a consumer good, intended for direct consumption by individuals and is classified as non-durable because it is consumed quickly.
Step-by-step explanation:
When looking for an example of a consumer good, we consider items that are intended for personal use or consumption by individuals. Among the options provided, a gallon of milk to use in a bowl of cereal is a clear example of a consumer good. Consumer goods satisfy our wants and needs, and they are typically classified as durable or non-durable. A gallon of milk is a non-durable consumer good, as it is intended to be consumed relatively quickly and does not last for an extended period. In contrast, stock shares, pet boarding business supplies, and professional equipment for a business such as an auto body shop do not qualify as consumer goods as they are designated for investment purposes or as capital goods for producing other goods and services.