You can add items to the shop in the costume editor, but you'll need to use advanced code. You can also add new sprites, but you'll have to code them separately, including position, click checks, and stuff like that. You'll also need to create some form of currency. Enjoy! Please like and favorite this project.
I saw the griffpatch platformer series and was inspired to add a shop to my game. When I finish the tutorial, I'm gonna backpack it and take it to the platformer series. I think the shop will make my game a lot more interesting and replayable.