Parents who have survived the 2's...

My goal as a parent is to be more regulated than my child. Most of the time I'm really good at handling typical 2 year old behavior. Meltdowns because the cup is the wrong color, etc? I'm riding the wave and staying calm. But, anytime we are out running errands he really struggles to listen and stay close. I give lots of verbal reminders that I need him to stay close to stay safe. Lots of praise when he does. Today while I was in line checking out, he sprinted away from me right out the door and might have run right into the parking lot if I hadn't caught up to him. It's impossible for me to stay regulated in that moment. I'm like the crazed mom running after him, yelling his name, yanking him by the arm out of danger. Then I beat myself up over it. Thankfully two older ladies in the parking lot saw us and just said "oh we remember those days!" Any suggestions on how to practice this skill with him? TIA