Are you immediately eating before riding or waiting like a half hour or more? Also, are you trying to go fast on your commute or taking it easy? Some people prefer a piece of fruit and a tall glass of water or coffee (something light) right before leaving. If you have some time (15 minutes to half an hour) intant oatmeal is good as well. I like a bit of protien like a small protien shake or two hard boiled eggs.

Some of what you decide is going to be trial and error. You will learn how certain foods will interact with you on your ride. Sometimes it also depends on the pace your are going.