Store bought dressing will last two to three months after opening if properly stored. The acidic vinegar based versions last longer than ones containing dairy. A Line V Neck Long Sleeves Dark Green Prom Dress With Split PSK082 US8 Custom Color Ball Gown Short In Front Long In Back Homecoming Dress Exquisite Short Sleeves Keyhole Back Tea Store bought Caesar dressing is pretty good for a quick meal at home, but you can make it so much better with one simple addition. You'll never skip it again.