Which item includes one piece per order under the sides category?

The item that includes one piece per order under the sides category is 1 egg roll. This is because side items at Jack in the Box typically have specified portion sizes, and an egg roll is traditionally served as a single unit. This serving size makes it easy for customers to understand what they are ordering and helps in portion control as part of a meal or as a snack.

In contrast, the other items listed are served in larger quantities. The crisp chicken strip is often sold in sets, which means customers would receive more than one per order. Similarly, 6 Mac n Cheese represents a bulk order, and 15 tiny tacos is also a larger serving. Such variations in serving sizes for these items highlight the unique serving style of the egg roll as a single serving option.