The phrase "add more items" is correct and usable in written English.
You can use it when instructing someone to include additional objects or elements in a list or collection.
Example: "Please review the shopping list and add more items if necessary."
Alternatives: "include additional items" or "insert more items".
The volunteers from New Delhi would add more items to that list once the afternoon was over.
Return to your inventory to add more items this way (unfortunately, you can't add several items at once from the list of checked out items).
The limitations of Warcraft 3 meant Dota has things like recipes [item combinations] – you couldn't add more items, there were only six item slots, so you had to do recipes.
It will be able to do this, according to its C.E.O., Marc Lore, partly because its profits will come from collecting annual membership fees of $49.99 rather than from margins on individual purchases, and partly because it will set its prices using special price-minimizing software, including a "smart cart" feature that lowers the total cost of an order as you add more items to a basket.
And there's a chance that as you start using new devices, you'll want to add more items as time goes on.
Children were told that each character's cup would "magically" add more items to a pile of objects already sitting on a table.
This collaboration will reduce unnecessary duplicative collecting through closer coordination of acquisitions with the goal of adding more items to the libraries of both institutions.
Today, however, a mastery of the old basics no longer suffices, because fundamental changes in the world economy have added more items to the list.
Revamping the website means not only adding more items but also making it easier for customers to search for what they want.
The restaurant recently added more items to its menu.
They suggested adding more items concerning other health aspects.
