Determine which product they would like to buy. Determine if they have enough money for the item. Count out the exact change or determine how much change they are due. Each child is given a set amount of change. The particular coins each is given is determined by which coins have already been introduced to them and which ones they have prior experience counting.
Beginners start with pennies only.
Each child is given a set amount of work in any subject that they need extra practice on. I usually use computational math skills. How many problems need to be completed before visiting the store is determined on an individual basis by the difficulty of the work for each child and how long it will take them to complete it. The teacher or a student helper is then the store clerk and takes the change from the student. The student must tell the clerk how much change they are due, if any.