I've been to a few fast food joints over the years. Hell, over the month. And I always get a "large" combo meal, because I like a lot of soda. You do get a lot of fries with the large size, but it's really all about the extra soda for me. In fact, if you could super-size the diet Coke, and keep the fries small, well that there would be a great option.
However, even with all of this experience, and all of the thought I have given this, I was absolutely floored, nay, disgusted, when I pulled the large fries out of the White Castle bag the other day.