Oatmeal does nothing for me. Even if I put vast amounts of PB or nuts and sugar in it, it does nothing. It doesn't get into my system fast enough, and happily mops up any fat I've eaten. I'm starving after about 10 miles.
I do need to eat on the ride, though, even if it's relatively short (10-15)--at least a chew thing at my turnaround. Apparently I'm not terribly efficient, or I'm not eating enough beforehand.