This study explores the production of bioplastic films from sugar cane bagasse, wood pulp waste, and boxboard waste using a three-step, sustainable process. First, cellulose was extracted from the biomass through a deep eutectic solvent (DES) pretreatment system composed of choline chloride, ethylene glycol, and oxalic acid (ChCl-EG-OA), which effectively removed lignin and enabled an efficient alkaline treatment for hemicellulose removal. Among the biomass sources, sugar cane bagasse yielded the highest cellulose content (72.86%), followed by wood pulp waste (43.82%) and boxboard waste (38.81%). In the second phase, optimal conditions for cellulose acetylation were established. Wood pulp waste achieved the highest cellulose acetate yield (81.25%), followed by boxboard waste (70.78%) and sugar cane bagasse (47.2%). Wood pulp waste-derived cellulose acetate also exhibited the highest acetyl content and degree of substitution (DS) at 2.83. In the final phase, bioplastic films derived from boxboard waste demonstrated superior mechanical properties, with a tensile strength of 11.23 MPa and elongation of 3.14%. In contrast, wood pulp waste-derived plastic exhibited moderate tensile strength (4.56 MPa) and minimal elongation (1.0%), while sugar cane bagasse-derived plastic showed the weakest performance. The study further highlights the adaptability of mixed-source bioplastics, as a blend of boxboard and wood pulp waste achieved a tensile strength of 7.26 MPa and elongation of 1.63%, illustrating the potential to enhance bioplastic properties through a biomass source combination. This approach contributes to the advancement of sustainable, high-performance bioplastics for a broad range of applications.