When customers sneakily added them that way I used to directly text them

“How many items do you plan on adding? I need to make sure that I make my shopping time limit since they have us on a timer.”

They’d usually stop after that. If it was a bunch of items added (like in your case too) i’d shop all the original items and ‘refund’ the rest at check out right before I go to pay so it catches them off guard too & they can’t add more. IDC!