Here are a few options you could use depending on the context:
* A row of cartons: This would be appropriate if the cartons are arranged in a line.
* A stack of cartons: This is suitable if the cartons are piled on top of each other.
* A shipment of cartons: This would apply if you're talking about a large delivery of milk cartons.
* A collection of cartons: This is a general term that works in many situations.
You could also use a more descriptive phrase like "a selection of milk cartons," "a variety of milk cartons," or "a supply of milk cartons."