This study explored the synergistic combination of silver nanoparticles (AgNPs), eucalyptus-derived nanofibrillated cellulose (NFC) and cassava starch to develop bionanocomposites with advanced properties suitable for sustainable and antifungal packaging applications. The influence of AgNPs synthesized through a green method using cocoa bean shell combined with varying concentrations of NFC were investigated. Morphological (scanning electron microscopy and atomic force microscopy), optical (L*, C*, °hue, and opacity), chemical (Fourier transform infrared spectroscopy), mechanical (puncture force, tensile strength, and Young's modulus), rheological (flow curve and frequency sweeps, strain, and stress), barrier, and hydrophilicity properties (water vapor permeability, solubility, wettability, and contact angle), as well as the antifungal effect against pathogens (Botrytis cinerea, Penicillium expansum, Colletotrichum musae, and Fusarium semitectum), were analyzed. The morphological analysis indicated excellent interaction between the bionanocomposites constituents. The maximum NFC addition increased the tensile strength of the bionanocomposites by approximately 283.93 % (14.85 MPa) while Young's modulus also showed a significant increase of 303.03 % (417.14 MPa), indicating increased stiffness. Water vapor permeability of the materials decreased by approximately 47.89 %. The materials exhibited hydrophilic properties while maintaining low wettability. Furthermore, the bionanocomposites demonstrated pseudoplastic (Ȳ = 0.59) behavior and an inhibitory effect against fungal pathogens. In conclusion, these innovative materials have the potential to transform packaging technology by serving as sustainable alternatives to petroleum-derived polymers while simultaneously adding value to agro-industrial waste.