Get everything onto one list
Lists come from recipes, from a planned week, or from you typing. However it got there, the list groups itself by aisle rather than by which recipe wanted the item, and the header keeps a running count of what is still outstanding.
Start a session, and the screen changes job
Shopping Mode is a session, not a view. While it is running the bottom of the screen stops being navigation and becomes the controls you want with a trolley in one hand: undo, finish, redo.
That is deliberate. Nothing about walking around a shop wants a tab bar, and an accidental tap into another part of the app mid-shop is genuinely annoying.
The list is now in shopping order, aisle by aisle, with big enough targets to hit while moving.
The progress header counts down. Undo is right there for the item you checked by mistake.
It holds your place for hours
A session survives you closing the app, taking a call, or putting the phone in your pocket for twenty minutes. It holds for about six hours, which covers any real shop including the one where you go for coffee halfway.
This is the detail worth knowing before you need it: you cannot lose your place by leaving the app. Check off as you go rather than saving it all until the till.