Fueling Before an AM Workout

Since I walk/run (I'm still uncomfortable really calling calling it a "run") first thing in the morning, I don't normally eat anything before I go--just drink some water and go! Since I've started running more and the humidity's increased, I've started trying to remember to eat a little something--right now that's 1/2 a Luna bar, because that's what was in the cabinet. I'll probably eat 1/2 a banana or some other fruit in the future.

Anyway, I've starting noticing a pretty significant difference in my performance on the days I forget to eat anything. Yesterday and today, I ran 6 min/walk 1 min x 4, plus 2 min running at the end. I was almost a full minute faster yesterday, which surprised me because I thought I'd run it faster today since my body was more used to it. However, this morning I didn't eat anything, and yesterday followed a rest day (unintended, I overslept). Plus I just felt super exhausted this morning. I can really see how it affected my performance! (The first and last intervals are warm up and cool down.)

If you work out early in the morning, do you eat something beforehand? What do you eat?