This work assesses the role of biomass and municipal solid waste in isolated energy systems. For this, La Réunion, a French overseas territory in the Indian Ocean with a population of about 850,000, serves as a case study. Methodically, the study assesses technical biomass-based potentials based on an island-wide digital landscape model, detailed information on land use, soil, and climate, and a dynamic yield simulation tool, while technical waste-based energy potentials are calculated from local data. In total, 9 crops, 11 waste streams, and forested areas are considered. The potential contribution of biomass and waste to the energy system is studied in three scenarios. In all, unsustainable outcomes are avoided by valorizing only crop residues and applying sustainable harvesting rates to forests. Depending on the scenario, biomass or waste based energy could cover between 19% and 22% of 2019 electricity demand compared to an actual value of 6% (2019). Furthermore, prioritizing the production of secondary energy carriers allows to meet 8% of 2019 energy demand in the transport sector. These results are in good accordance with previous studies and scenarios on Réunion's energy transition. Given its bottom-up approach based on standard geoinformatic data, the proposed method is in principle transferable to other isolated regions, also in developing countries. A first, high-level assessment of four comparable island (states) shows that in three cases similar contributions of biomass and waste as in Réunion can be expected. As a next step, the purely technical assessment shall be complemented by economic considerations.