I designed this activity based on requests from my JTEs that we practice "useful real English." It requires a bit of preparation beforehand with respect to printing things out and getting organized, but it's worth the effort. The students had a lot of fun doing this. I also highly recommend that you make some fake money to give to the students to help them get into it even more. I just used a picture of an American dollar and replaced George Washington with a picture of myself, it was really entertaining for my students to use money with a crazy picture of their ALT on it ;)
First, I do a simple warm-up (I really like [this one](https://www.altopedia.net/activities/2682-l-r-telephone) ). Then, I ask the students to move their backpacks out of the way, since I encourage them to walk around during this activity.
I alternate rows of shopkeepers and customers. Pass out the corresponding instructions and briefly explain their roles. Then, pass out the menus to the shopkeepers. I have three different shopkeeper menus, but you can do as many or as few as you want. Pass out a random amount of money to each customer. You can tell them to keep a reciept on the back of their instruction handout. If you have a small class, you could print out some stock for each shopkeeper. Make sure they generally understand their roles, and then set them free! This activity leaves a lot of freedom and interpretation to the students.
During the activity, the JTE and I were "government workers" who could give jobs to students who ran out of money. By performing some simple task, customers can earn money so they could keep spending. We would take "taxes" from the shops to refill our stashes.
I walked around and gave them suggestions and encouraged them to be creative. They ended up haggling, hiring each other, (I even got some gambling...), and having a LOT of fun. My students are at an academic high school, so they're high level and really enjoy unstructured and challenging activities like this. You could easily decrease the difficulty by adding Japanese instructions and/or giving them scripts. I hope you and your students can enjoy this role playing!
More of a lurker than a commenter but I wanted to say my students LOVED this activity, they're SHS very low level English but they got a huge kick out of negotiating in English and this activity was the most motivated I've ever seen them to use English, so thank you so much for posting this activity!