You can definitely do as you suggest. Taking food back to the room is easy and welcomed. (Some things can be stocked up the day before and/or kept in the fridge.)
Just wanted to add one thing that hadn't occurred to me before I started cruising. On the ship, it is much easier to mix and match. Everything is so close, and unlike normal vacations don't require cars etc. So we often got a little bit (coffee, juice, fruit maybe?) delivered to the room first thing (they make you pick a delivery window, but for us they always hit the beginning of it), then a couple of the earlier risers would hit the buffet, then the later risers would hit the sit down breakfast, or vice versa, or in the case of my one son, sometimes all three. It's just a set of options you don't usually have when everyone is tied to a car and a driver or something.