For food, I'd go back upstairs to the International Terminal. More options there. The domestic terminal has a smaller food court. The only issue is whether the shops are open as I think if you land early in the morning. However, as mentioned, Maccas are everywhere and open all the time.

The walk is good exercise, particularly after a long flight. Follow the line on the footpath. I may even be fun for the kids. If the weather is bad, there's a free bus.