My 2c.
I swear by caffeine. I will have a latte if I have a couple of hours pre-ride. The skim milk keeps the espresso from being too harsh on my stomach and provides some protein. Otherwise I drink diet coke before I ride. No sugar that long before riding.
I am a relatively new cyclist and only have a few rides > 3 hours. I don't ride every day. My usual diet is low fat, high carb focusing on fruits,vegs, whole grains. Usually I just take water on a ride; for my most recent 50 mile ride I took a bottle of G2 and a powerbar also. I seem to average 13.5 mph whether I'm riding 5 miles or 50. These are rides where my performance is important to me but I'm not redlining or maxing out. It sounds like your intensity was much higher.
The only time I bonked was at a swim meet where I had 5 events in 6 hours, along with warmups/warmdowns for each event. It was absolutely a miserable day - I got chilled and couldn't warm up, had a 200 mile drive after dark to get home, and I was on the verge of tears. I started that day already depleted and didn't have much breakfast and had no snacks. This sounds really bad but after that I started eating a small bowl of ice cream for breakfast about 4 hours before my first event along with coffee. It had a lot of calories, more staying power than a breakfast of only simple carbs, and it was low-volume so it did not mess up my streamlining. Away from home an Egg McMuffin is what I get.
One of my worst swim meets was where I hit a breakfast buffet and filled a few plates. A boat anchor would have been a better meal. I was bloated, lethargic and slow the rest of the day.
Other thoughts:
* Chocolate milk immediately afterwards is a good recovery drink.
* Alcohol can take 36 hours to process before you can ride well. After a good night of margaritas and a morning workout, I've tested with a blood glucose of 36.
* If you know you're in trouble, it might be time to bail rather than tough it out.