<p>While chitosan-based films are widely studied for food preservation, their practical application is often limited by inherent limitations in stability of the material, antibacterial efficacy, and long-term preservation capability. Here, we present an innovative one-pot fabrication of a multifunctional, biodegradable food packaging film based on a chitosan-potato starch matrix synergistically enhanced by calcium ascorbate (CA) and Au@Ag. CA acts as both an ionic crosslinker and an active antimicrobial/antioxidant additive, while the embedded Au@Ag nanoparticles synergistically reinforce the functional performance of the composite film. The resulting exhibits considerably improved mechanical strength (tensile strength increased from 7.58 to 8.76 MPa) and enhanced water barrier properties (WVTR reduced from 0.312 to 0.271 g·m⁻²·h⁻¹). Notably, it demonstrates high water stability, nearly complete UV-blocking (≈99%), and the composite film exhibits considerably enhanced ABTS and DPPH radical-scavenging activities compared to the control CS/PS film (<i>p</i> &gt; 0.05). Antibacterial testing shows 100% inhibition against Escherichia coli (<i>E. coli</i>) and Staphylococcus aureus (<i>S. aureus</i>). In practical preservation tests, the lower water contact angle (WCA) of CS/PS/CA/Au@Ag film promotes strong adhesion to the grape surface, which enhances contact-active antimicrobial efficacy and results in a longer shelf life than commercial polyethylene (PE) wrap. Combined with excellent biosafety and soil-degradability, this rationally engineered composite represents a sustainable, high-performance alternative to conventional petroleum-based packaging for food preservation.</p><p></p>