If you mean a container:
* Individual items: If you're talking about a carton holding multiple items, you could say "individual items" or "loose items."
* Bulk: If you're talking about a carton holding a large quantity, you could say "bulk" or "wholesale."
* Unpackaged: If you mean something not in a container, you could say "unpackaged," "loose," or "uncontained."
If you mean a specific type of container:
* Bottle: If you're talking about a carton for milk or juice, "bottle" could be an antonym.
* Can: If you're talking about a carton for soup or vegetables, "can" could be an antonym.
* Bag: If you're talking about a carton for eggs, "bag" could be an antonym.
If you mean a specific material:
* Glass: If you're talking about a cardboard carton, "glass" could be an antonym.
* Metal: If you're talking about a cardboard carton, "metal" could be an antonym.
Ultimately, the best antonym for "carton" depends on the specific context.