Things to stuff bone with?

I use an empty, cleaned marrow bone as a sort of Kong for my Golden. I put one banana slice on one side, fill it, and then plug the other side with another banana slice, then I freeze it. My question is, does anybody have any stuffing ideas that are healthy as an occasional treat? I have been using peanut butter, treats, and a little bit of cheese but I'd like some more variation. I'd like to try yogurt or cottage cheese as well, but we don't have any at the moment.