Like a few have alluded to, how one fuels up on a ride depends on what you eat before and after (throughout your week of workouts). Provided you have a good diet with enough carbs I submit that it would then depend on mileage and your route (effort). I have taken to bringing a bar or fig newtons or something along just in case.

I still consider myself a new rider learning all the ins/outs, but have been into general fitness since my mid-teens (I'm 45). I have found that my previous weights and ~30-45 minutes carido interval training diet does not support my new cycling needs (I have been generally following the Abs Diet-type approach). Last Monday I followed my normal diet and only packed water for my 30 mile ride. Halfway in I really started feeling sluggish. My buddy kept slowing down to pick me back up. Not sure a few carbs during the ride would have really helped. Next ride two days later I modified my diet to include about 30-45 grams of carbs with each meal and snack. I also filled one of my two water bottles with Powerade. My buddy could not keep up! I had crazy energy! Now I am just trying to sort out a complete approach that is "just enough" so I don't actually gain weight yet have plenty of energy.