Grocery shopping
How many different groceries do you buy in shop? Do you ever shop for parties? How do you remember all the groceries you want to buy? Do you use a paper sheet? Or you keep everything in your mind and then you go home and realize that you forgot a banana?

Make a list
You can easily solve this problem by creating "Shopping Challenge". Anytime you think of an item that you want to buy - just add a new task to this challenge. When you go to the shop you will have a whole list of items in place and you can check tasks when you pick item.

Offline app
Cool thing is that all checked items will go to the bottom of your list so that you can focus on those items that are not picked up yet. Plus it works offline so it's safe to go to underground shop.