This paper presents results of research into polypropylene based wood plastic composites reinforced with food industry and forestry by-products, identified as being particularly abundant in Australia but underutilised, viz. macadamia shells, pine cones and eucalyptus capsules. The present study considers and explores the suitability of these materials for high-moisture environment furniture panel applications. Results are presented for the relevant physical and mechanical properties and are compared with a conventional wood plastic composite utilising radiata pine as the filler. The water absorption and swelling were generally lower in the forestry and food industry by-product composites than in the conventional radiata pine composite with the best results being obtained for the macadamia nut shell composite. The mechanical properties were however poorer than those of the conventional wood plastic composite. Nonetheless, it is considered that the forestry and food industry byproduct composites do provide a viable material and have the potential to become a sustainable replacement option for high-humidity environment furniture panel composites. This would provide much better utilisation of these currently undervalued agricultural waste resources.