Device to squeeze last yogurt out of carton
As the response to my comment didn't say it wasn't the boxy aseptic packaging (used for soy/rice/coconut/almond milk, broth/stocks, shelf-stable milk, milk and juice cartons, etc.), I'm going to assume it was, and move it to an answer:

Square or rectangular packaging should have two little ears on the bottom of the package.  If you pry them up, you'll find that the box is really a tube with one end sealed, like a tube of toothpaste.

I've not tried this for the aseptic packaging (as I've never gotten viscous items packaged that way), but you might be able to use the same trick for toothpaste tube:


With the open container on the top of the counter, press the sealed edge on a sharp corner of the counter (not one of those really rounded over ones, as those don't work as well).
Place your hand on top of the container, and push it both down and off the edge of the counter.
Once you have enough over the edge to grab, grip it and pull it down (or at least at a downward angle).  This will force the contents towards the open end of the tube.
Once the contents come up to the container's opening, squeeze in into a bowl or other vessel.  (it can help to fold the tube a bit, so that squeezing doesn't force it back into the end that you just cleared out).
Repeat until you've gotten all that you can out.


It might seem strange, but once you've gotten the hang of it, if you have a good edge to work it against, it's quite easy.  If you don't have a good edge ... you might try against the rim of a sheet pan.