You stop what you are doing and tell the child that you are going to take him to the car and get a spanking. Don't let them talk you out of it. Once in the car talk with them and follow through.
1. Don't take the kid. Yeah, I know it's tough, but really, why put yourself through it? Leave the kid at home with a babysitter, work out a swap with the family down the street, whatever. It will be easier in the long run.
2. Don't take the kid when they are tired. Too many people haul kids around when they are worn out and not ready for it.
3. Prep the kid. Sit them down before you go and have them help make the shopping list, explain what you are getting, what stops are going to be made, and make sure there is something they want to do as well.
Aggie80