Bon voyage! Although I don't think I can get up so early...

I think you can go window shopping at Narita airport. Japan is notoriously expensive, so I don't suggest you buy anything. However, you might be able to find some kiosk selling bite-sized Japanese delicacies or a small bento set for perhaps a few hundred yen to two thousand yen. I don't exactly know how much things are sold in the airport, but as a reference point, a 0.5 liter carton of milk usually sells for 150 yen at Japanese convenience stores.