Petroleum-based plastics are harmful to the environment, and although PLA/starch composites are biodegradable, they are not antimicrobial. This systematic review of 91 studies examines whether plant biomass extracts such as pomegranate peel, olive leaf, betel leaf, grapevine cane, and chicory root can fulfill that role in food packaging. Minimum inhibitory concentrations range from 1.25 to 3.0 mg/mL, while film activity is reported as inhibition zones of approximately 9–16 mm; these two assays are not equivalent. Loadings range from 2 to 10 wt%. In individual studies, tensile strength ranged from 8.6 to 34.5 MPa, below that of neat PLA (50–70 MPa), whereas water vapor permeability (WVP) was reduced by about 55% (olive leaf, grapevine cane) and oxygen permeability by 70% (betel leaf, coated PLA); UV blocking reached 65–66% (tannic acid). These are single-value estimates, not pooled values. PLA-containing systems degraded in 13–60 days, compared with approximately 180 days for neat PLA. The main gaps are: PLA–starch incompatibility, migration testing (less than 15% of studies), pilot-scale validation (less than 5%), and the absence of predictive models. Priority directions are controlled release, synergistic extract combinations, green extraction, and multi-scale computational modelling validated by defined experiments.