Premade pie crusts
Premade dough and premade graham cracker crusts are some of the worst offenders for added trans fats. Also avoid frozen vegetable-and-meat potpies or completely assembled frozen pies—a single serving can contain between 2 and 4.5 grams of artery-clogging trans fats!
True, margarine is made with lower-in-saturated fat and cholesterol-free vegetable oil instead of dairy or animal products, but in order for margarine to maintain its solid form at room temperature (like butter does), it has to be loaded up with hydrogenated oils that are high in trans fats. Several butter alternatives have made the shift away from trans fats and now even include cholesterol-lowering plant sterols.