MycoBag is a material exploration project that proposes a new construction system based on bioplastic bags filled with agricultural waste and mycelium. Through physical prototyping and performance testing, the project investigates the structural behavior, material adaptability, and logistical efficiency of this system as a way to challenge the inertia of conventional construction materials and methods. At the heart of the project lies a deeply intuitive and age-old gesture: storing something valuable in a bag. Across cultures and throughout history, the act of placing food, tools, or goods into a bag has represented protection, portability, and preparation for future use. This project reclaims this familiar logic and elevates it into a construction technique, one that is accessible, scalable, and regenerative. The combination of bioplastic and shredded agricultural waste becomes self-reinforcing once inoculated with mycelium, simplifying the production chain and reducing the need for specialized labor or infrastructure. The process is designed to integrate effortlessly with existing agricultural routines, from rural regions from Kenya, Punjab, or Indonesia to industrialized contexts such as the United States and France. This seamless compatibility allows the system to scale quickly and adapt to various geographies, climates, and economies. As a carbon-negative, low-tech, and high-impact material system, it enables anyone, anywhere, to build and create with what is locally available, turning agricultural surplus into shelter while storing CO₂ in the built environment. It is a solution for both rural and urban futures, offering a new architectural language rooted in care, circularity, and collective intuition. Ultimately, innovative system envisions a world where ecological responsibility meets design empowerment, where everyday people, not just experts, can become agents of spatial and environmental change.