Tree structured shopping lists
One thing that would be handy for shopping lists would be a tree structure, so you could put "milk", "cheese", and "eggs" under the "Dairy" node, and "lettuce", "carrots", and "apples" in the "Produce" node. (For book shoppers, author names would be nodes and then lists of books to look for would be leaves under it-- or names of series in a subnode.) Closed nodes would just show their name; open ones would show their contents. If all children of a node are checked off, then the node would show as checked off.