On his most recent trip to the running store, Andy noticed that the water bottles for his favorite hydration belt were on sale. They were usually priced at $8, but they were on sale for $5.

The store owner told Andy that he was surprised that people were not only buying more water bottles due to the sale, but also more of the hydration belt, even though the belts were not on sale.

Based on the scenario above, what type of goods are the water bottles and hydration belts?