The best grocery list is the one everyone in the house adds to. Both of these are free, update on every phone at once, and sort themselves into aisles or checkboxes.
Use the Groceries list in Apple Reminders
Where to find it: Reminders, Add List, List Type, Groceries, then the Share button
A list set to the Groceries type sorts each item into a section such as produce or dairy as you type. It needs iCloud switched on for Reminders. Share it, and everyone's additions land in the same list.
Share a checklist in Google Keep
Where to find it: Google Keep, New list, Collaborator
A Keep checklist shared with your household works on iPhone and Android, and everyone you add can tick items off or add new ones.
Put the list where the shopping starts
Where to find it: Your home screen, add the list app's widget
A widget on the home screen puts the list one tap away, which is the difference between a list people use and one they forget.
