The greatest enemy of meat, dairy, and produce is warmth, so the colder you can keep your food, the better. Start your shopping in the middle of the store, where the pantry items are, so refrigerated and frozen foods won't sit too long in your cart. Harold McGee, the author of Keys to Good Cooking
, suggests keeping a cooler in your car and placing meat, seafood, and milk in it for the ride home. You can also ask that especially perishable items, like fish and shellfish, be bagged on ice. If you don't have room for a car cooler, McGee suggests bagging frozen and cold foods together. At home, check the temperatures of your fridge and freezer (they should be set between 35 and 40 degrees and at zero, respectively). For a fast test, feel ice cream—if it's soft, your freezer is too warm.