The mechanical and physical properties of the bionanocomposite films based on κ-carrageenan (KC)–gelatin (Ge) containing zinc oxide nanoparticles (ZnONPs) and gallic acid (GA) were optimized using the response surface method, and the optimum amounts of 11.19 wt% GA and 1.20 wt% ZnONPs were obtained. The results of XRD, SEM, and FT-IR tests showed the uniform distribution of the ZnONPs and GA in the film microstructure, and suitable interactions between biopolymers and these additives, which led to increasing the structural cohesion of the biopolymer matrix and improving the physical and mechanical properties of the KC–Ge-based bionanocomposite. In the films containing gallic acid and ZnONPs, an antimicrobial effect was not observed againstE. coli; however, the GA-loaded and optimum films show an antimicrobial effect againstS. aureus. The optimum film showed a higher inhibition effect againstS. aureuscompared to the ampicillin- and gentamicin-loaded discs.