Which side can be substituted for a small upcharge?

The correct answer highlights the flexibility of menu choices at Metro Diner, indicating that substitutions for sides can be made for a small upcharge across all the options provided. This policy allows guests to customize their meals according to their preferences, enhancing their dining experience.

By allowing substitutions for different sides, the diner caters to various tastes and dietary needs, whether a customer prefers the heartiness of potatoes, the lightness of rice, or the freshness of salad. This adaptability is common in casual dining establishments where customer satisfaction is prioritized, recognizing that diners may have personal favorites or specific dietary requirements. This approach positively impacts overall guest enjoyment and encourages repeat visits.