Procedure
If you are practising language, review useful structures with the class first, e.g. 'I'm looking for a…', 'I wonder if you can help me, I…', 'How much is that?', etc.
Hand out the cards to the students making sure there is an equal number of shopping lists and shops.
Give the learners time to read their cards and ask you about any problem language. They also need to think about what they are going to say, and what language they will need. You can group the shoppers together and shop owners together to do this.
Point out to the shop owners that they may need to decide how much their products cost before starting.
Set up your classroom to represent a street, with each table being a shop if possible. Ask the learners who own a shop to prepare a card (folded piece of paper) saying what shop they own.
Start the role-play. The shoppers need to find everything on their lists and complete their short task also.
Monitor the activity for interesting language or for problems, which you can feedback afterwards. Try not to intervene too much at this stage.
Keep the role-play going until enough shoppers have completed their tasks.
Put the class into groups and ask them to explain how the shopping (and selling) went, and what problems they had.
Feedback open class on any interesting language points.
N.B. These cards can be exploited in any way, e.g. as practice after looking at interactional language or common vocabulary, as a spontaneous speaking exercise, or as a diagnostic for you to see what your learners know. You can review the language needed for the task before or after the role-play, depending on your aims.