In the same meal, would you ever eat or serve rice and potatoes, or macaroni and corn, or venison and rabbit, or chicken and duck?

Yes. If that is what I wanted to have at the time.

Not only in the same meal, but in the same dish. 

Only if they are combined to make one beast or one starch or one vegetable or one fruit or one dairy product.
Take the Jack-0-lope, for example.  There are two types of meat combined into one beast that you can eat if you catch one.
Tangerines are a combination... I think..??
Potato bread is a starch example
Goat cheese is another... am I reaching here?

I do attempt to cook and create at least one balanced meal every day for Don and myself.

One of each is plenty.  No need to overwhelm your taste buds or body with one and not the others.

Nope.
For a main meal I choose one of each from specific food groups; starchy carb, protein, the onion family, and greens.
My meals may often contain other elements such as mushrooms, root veggies, fruit, nut, herbs and spices, oils and vinegar.

Mac and cheese with corn sounds good.
Have you ever heard of turducken?