Which mix-ins do not change in portion amount regardless of the situation?

The selection of Double Stuf, Coffee, and Malted Milk as the correct answer is based on the understanding that these mix-ins have a consistent portion amount that does not vary with the size of the order or the preparation context at Five Guys.

Double Stuf, as associated with the Oreo product line, typically comes in a standard portion. Coffee and Malted Milk also reflect specific amounts that are meant to provide a uniform flavor experience across different servings. This consistency is important for maintaining the standard flavor profile and quality that customers expect with each order.

In contrast, the other options include mix-ins that may vary in portion size depending on customer preference or specific menu items. For instance, ingredients like Peanut Butter, Jam, Honey, and others can be added in different quantities based on a customer's taste, which highlights their variability and flexibility, unlike the steadfast portions of the items in the correct answer. Such distinctions help Five Guys in delivering a consistent product while accommodating different customer preferences for specific mix-ins.