https://www.templatemaker.nl/
This is a great source for templates of many different packaging designs. All customizable and available to download in pdf, or svg formats. (You have to click on the "More Options" link to get all three format options. It defaults to pdf. And, they are all free to download.
Also can be used to figure out shapes for modeling.
Here is a sample I was working on for my little show next month:
Oh the irony, I'll be selling 3d printed, plastic versions of my favorite paper creations, lol!!!