The rapid growth of the global population has led to significant environmental impacts, driven by the unsustainable extraction of resources and waste generation. To address these challenges, the valorisation of by-products from different industries is crucial for maximising resource efficiency, reducing waste, and promoting sustainable practices. In this study, a comprehensive characterisation of the physicochemical properties of plant-based by-products, including rice husk (RH), oregano stalks (OS), eucalyptus leaves (EL), and almond shells (AS), was conducted. The analyses of the residues showed that, despite the similarities regarding cellulose and lignin content in all materials, RH and OS present a higher cellulose content, while EL and AS contain a greater percentage of oils. Additionally, calcium and potassium were identified as the metals at higher concentrations in all residues. The EL and RH present significant hydrophobic properties compared to the other analysed residues, showcased by their lower wettability. The morphological analyses of the waste residues revealed that OS and RH particles exhibit fibrous characteristics with heterogeneous sizes, while EL is a blend of fibrous and amorphous particles, and AS is composed of smaller particles with irregular shapes. All the residues retained their antioxidant properties over a 12-month storage period, with no degradation due to grinding. The composition and physicochemical properties of these residues highlight their potential to be used in distinct industries, including construction, transport, and textiles, promoting a circular economy and supporting a more sustainable environment.