Underutilized co- and by-products are upgraded into materials with functional properties. The utilization of mushroom farming residues is investigated, specifically mushroom residues and spent mushroom substrate – whose chemical composition is determined – to produce cosmetic face masks, packaging films, and oil sorbents. Flexible mushroom sheets exhibit conformability and antioxidant activity between 82 and 94%, and better tensile strength in comparison with commercial cosmetic masks, making them suitable for such applications. Plasticization with glycerol increases the flexibility and tensile strain from ≈1 to 45% and moisture sorption from 32 to 100 wt.%. Spent mushroom substrate pulp yields stiff and strong rigid sheets with Young's moduli of 5 GPa and tensile strengths of 42 MPa. These sheets show 100% antioxidant activity, having hydrophobic behavior and oxygen barrier properties in dry conditions, and thus are promising for bioactive packaging applications. Foamed spent mushroom substrate sorbents demonstrate high affinity for both oil and water, with a water and oil uptake of 21 and 28 times their weight, respectively, while maintaining structural integrity. These properties make the foams viable as bio-based oil sorbents, highlighting the potential of by-products for advanced functional materials.