They're shelf stable for so long because they contain this menagerie of chemical additives.
"Water, Milk Protein Concentrate†, Calcium Caseinate†, Contains less than 1% of High Oleic Sunflower Oil, Natural and Artificial flavors, Inulin, Cellulose Gel and Cellulose Gum, Salt, Sucralose, Acesulfame Potassium, Carrageenan, Tripotassium Phosphate, Dipotassium Phosphate, Sodium Hexametaphosphate, Vitamin and Mineral Blend (Dl-alpha-tocopheryl Acetate [Vitamin E], Zinc Glycinate Chelate, Ferric Orthophosphate, Vitamin A Palmitate, Niacinamide, Phytonadione [Vitamin K1], Potassium Iodide, Cholecalciferol [Vitamin D3], Copper Gluconate, Calcium D-Pantothenate, Manganese Sulfate, Sodium Selenite, Biotin, Sodium Molybdate, Folic Acid, Thiamine Mononitrate [Vitamin B1], Cyanocobalamin [Vitamin B12], Pyridoxine Hydrochloride [Vitamin B6], Riboflavin [Vitamin B2], Chromium Polynicotinate), Magnesium Phosphate, Sodium Ascorbate, Choline Chloride."
When we're going out for a few days we just put some heavy cream into a glass milk bottle and keep that in the fridge.