Empty Container

It sounds like you're referring to a common item found in restaurants in the United States called a "to-go container" or "take-out container." These are typically made of plastic or paper and are used to pack food for customers who want to take their meals on the go or eat them at home.

To-go containers usually have a lid and a bottom section that can be separated to make it easy to carry and transport food. They come in various sizes to accommodate different types of meals, such as sandwiches, salads, soups, and entrees. Some restaurants may also offer biodegradable or compostable options to reduce their environmental impact.

In addition to their practical use, to-go containers have become a staple of American culture, often featuring iconic logos or branding of popular fast-food chains or restaurants. Some people even collect them as souvenirs!

So there you have it - now you know a bit more about the mystery item you saw in US restaurants!