Select a word or signal which you can both use to get the immediate attention of the other.
Role play at home how to act in the store.
Keep it simple such as a choice of a favorite snack food, or a stop at the park. Promise to read a story or play a game at home. When we leave, you can select a package of gum if you remember the rules. Bring a story book for the child to look at. Keep a supply of little action figures or small manipulative toys handy.