PLA composite films with improved mechanical, barrier and antibacterial properties were prepared by solution casting using silane-functionalized nanofibrillated cellulose (MNFC) and chitosan-encapsulated zinc oxide nanoparticles (CS-ZnO) as dual fillers. Nanofibrillated cellulose was first soaked in an aqueous solution of zinc chloride and aluminum chloride to disrupt its hydrogen-bond network, then grafted with KH-570 (γ-methacryloyloxypropyl trimethoxysilane). This converted the cellulose from type I to type II polymorph and improved its compatibility with the hydrophobic matrix. The CS-ZnO nanohybrid was obtained by alkaline co-precipitation followed by chitosan coating, yielding a ZnO crystallite size of 18.4 nm from the Scherrer equation, with the coating limiting agglomeration. Films containing 1 to 15 wt% MNFC at a fixed CS-ZnO content of 0.25 wt% were characterized by FTIR, XRD, DSC, TGA, SEM/EDS, tensile testing, water vapor transmission measurement, and disk diffusion assay. At 5 wt% MNFC, the tensile strength reached 31.40 MPa, an increase of 113% over neat PLA, crystallinity rose from 8.67% to 35.2% and WVTR fell by 79.3% to 3.15 g/m²·24 h. Inhibition zones of 18.3 mm against E. coli and 15.7 mm against S. aureus were obtained, although the mechanisms responsible for that activity were not investigated here and are discussed only with reference to the literature. MNFC therefore acts as a nucleating and reinforcing filler, while CS-ZnO supplies antibacterial activity, and the combination offers a workable route to multifunctional biodegradable packaging films.