Google Keep is one of Google's quieter successes. The notes and to-do app has a ton of awesome, buried features. For example, you can add items to your shopping list without ever opening the app. If you want to add something to your shopping list, simply say "add [ITEM] to my shopping list" in Android's voice commands. The Google Keep app will then open and automatically add that item to your list.
As Reddit user shiftingtech points out, technically this works with any named list in Keep. If you have a list named "Holiday" you can add entries by saying "add [ITEM] to my holiday list." If you then want to open that list later, you can say "Open my [NAME] list" to pull it up directly.