We (as being a family of 7) would always eat at Columbia Harbour House.
With CHH, we would get 1 meal (fish & chips, chicken strips, or a mix) and split between two of us. If we wanted more, we generally got another side of fries.
I have begun to learn that most of the meals can be split between two people. Hamburgers are decent size, pizza can be split. And like I said, you can always get an extra side.
If you go during the summer, you will eat a lot less than you think you will.
One of the biggest things that my sister and I did was *gasp* buy a bottle of Coke or water and refill it with fountain water. As many can tell you, WDW water has an interesting taste. You have to get use to it (my sister and I drank so much one summer, that we came back home and couldn't drink tap water from here, and I'm not kidding you it was in like 98 or something and I didn't get used to drink our tap water til about 2000).
I agree with bringing snacks. I carried granola bars and breakfast bars on me.