Thanks everyone for your suggestions!!!
Wow I'm so pleased he isn't the only one that eats directly from the carton! He really is a pretty neat and tidy person but I thought declaring that people might imagine him a neanderthal caveman! I love all the ideas... I do indeed have an empty container, and measuring is one way and taking it apart is the second option....I didn't think about using the insulbright, of course that's a great idea. Since he generally just grabs a terry dish towel I thought batting was what I was going to use.
I'm going to combine them and come up with an insulated holder....will let you know what the outcome is.