By-products from the agro-food industry can serve as innovative sources of natural ingredients in the reformulation of traditional foods, enhancing their overall quality, extending secondary shelf-life (SSL), and mitigating food loss and waste. This study aims to evaluate the effect of the addition in a ready-to-use meat pâté of an olive vegetation water phenolic extract (OWVE) at two concentrations (250 mg of phenols per kg of product (MP1) and 500 mg of phenols per kg of product (MP2)). Physicochemical and sensory properties and the antioxidant activity of OWVE-added pâté samples were evaluated and compared with a control sample (CTRL; without antioxidants), simulating the retail storage conditions typical for products sold loose in deli counters. The evolution of key quality parameters was monitored during the SSL at various intervals: 0, 1, 2, 3, 4, 7, 8, 9, 10, and 11 days after the packaging was opened. The addition of OWVE effectively reduced the formation of primary and secondary oxidation products, thereby enhancing the oxidative stability of the lipid fraction. The formation and accumulation of aldehydes C6–C9, which are responsible for the "rancid off-flavour", were significantly minimised in the OWVE-added pâté samples in a dose-dependent way. Additionally, the OWVE-added samples demonstrated significantly higher antioxidant activity and α-tocopherol content compared to the CTRL at every assessed time point. No sensory defects were detected in any of the samples; however, a more pronounced olive flavour was noted in the MP2 samples compared to MP1 and CTRL. The findings of this study suggest that OWVE could serve as a promising natural preservative for food formulations with complex compositions. This highlights its potential usefulness in countertop gastronomy products, allowing for the extension of SSL without the need for synthetic additives. This approach offers a sustainable solution for reducing food loss and waste in marketing and home preservation practices.