<p>Ready-to-drink (RTD) nutritional supplement beverages are widely consumed in clinical and long-term care settings; however, quantitative links between vitamin stability, industrial packaging–processing practices, and nutritional shelf life remain limited. In this study, the degradation behaviors of vitamin C and vitamin B1 were investigated in RTD beverages processed and packaged using two commercially relevant systems, Tetra Pak^® cartons and retort-sterilized metal cans, across storage temperatures of 20, 37, and 55&#xa0;°C. Owing to differences in thermal severity, the two systems resulted in distinct post-process vitamin concentrations, which were explicitly considered in subsequent kinetic and shelf-life analyses. Vitamin degradation rates increased with storage temperature and were adequately described by first-order kinetics. At moderate storage temperatures, vitamin C retention differed between the two packaging–processing systems, whereas vitamin B1 exhibited rapid loss irrespective of packaging. The temperature dependence of degradation rate constants followed Arrhenius-type behavior, and complementary thermodynamic insights were obtained using the Eyring model. Nutritional shelf life was defined as the time required for the vitamin concentration to decline below the declared label-claim level, which was set at 100% of the declared claim in this study. Under this criterion, metal cans were associated with longer predicted shelf life for vitamin C, while vitamin B1 generally emerged as the limiting nutrient across packaging systems. Overall, accounting for processing-related losses together with storage temperature and packaging characteristics provided a practical framework for evaluating vitamin stability and nutritional shelf life in RTD nutritional supplement beverages.</p>