What is the purpose of filling juice containers when opening the bar?

Filling juice containers when opening the bar primarily serves the purpose of ensuring fresh mixers are available for use throughout the service. Fresh mixers, such as various types of juices, are essential for creating a wide range of cocktails and mixed drinks that customers may order. Having them readily accessible not only helps streamline the bartending process but also enhances customer satisfaction by providing high-quality and tasty beverages.

While creating cocktails is a related activity, it's dependent on having the mixers prepared beforehand. The option regarding providing customers with garnishes focuses on a different aspect of drink preparation. Similarly, cleaning the bar area, while important, does not directly relate to the function of juice containers. Therefore, ensuring that fresh mixers are on hand is the critical purpose of filling juice containers when preparing to serve customers.