If someone had a product line that needed a package for each unit sold, how would you find where to get the packages for your product made?

There must be times when the product is made and packaged all in the same factory AND times when that doesn’t happen. In the latter case, who would someone who needed packages for their products go to?

In case anyone doesn’t get the question, here’s an example:

Someone owns a pizzeria that does delivery, and so they need boxes to send the pizzas in. Who makes the boxes? Not just generic ones, but ones with the company logo, a custom design, product information, etc.

I’m not just asking about cardboard boxes, though, so anyone with info on other types of packages can still post that info.