If you were limited to choosing only three crops to sustainably farm in an arid, inhospitable environment, what would they be and how would you decide? This interrupted case study places students in the role of a proposed self-sufficient Martian colony that requires an optimized profile of food crops. After students form small groups, they discuss the factors that affect sustainability of a food supply, determine criteria for selection of crops to grow, and rank crops using these criteria. Lists of criteria and of foodstuffs are provided, but the case can easily be transformed into a problem-based learning (PBL) case by having students research and generate their own lists. The case includes questions that walk students through the selection process and require them to explain why they chose their criteria and how those criteria apply to their chosen foods. The case is designed for undergraduate students at the introductory level in courses in astronomy/astrobiology, food science/nutrition, agricultural engineering, or any discipline where sustainability is a key theme.