For any ride over 2 hours, I start pushing 250 - 300 calories/hour at the 60 - 90 minute mark. Usually, it's half a Clif Bar, a bottle of Accelerade, and an Accel Gel. I pretty much graze constantly after an hour and a half of riding.
I also take 1 - 3 Endurolyte capsules every 60 - 90 minutes depending on how much I'm sweating.