Ok, I have to admit that I simply have to eat during a long ride.  When  
you figure that I left this Sunday at 8:30 am and did not get back to my  
house until about 2:30 pm, that's a long time without eating (compare that  
if I was at work, I'd have eaten two meals and a snack in that time  
period).  I ate/drank two bars (270 cal, 30g of carbs), one before the  
ride, one during, and had four drinks -- three with maltodextrin, lite  
salt, and protein, and one with maltodextrin and lite salt.  There are  
about 10g carbs and 10g protein in the carb/protein drinks, but I had  
probably 20g carbs in the carb-only drink.  My biking data:

Distance:  62.4 miles
Total time:  6:48:24
Altitude climbed: 4820 feet
Avg. speed:  11.4 mph (calc. made while moving)
Max. speed:  42.4 mph (it rained the entire time I rode, so I couldn't go  
fast downhill)
Avg. HR:  156 (84% of Max HR of 186)
Max. HR for this ride:  196 (incorrect -- a spike around HRs that are  
lower)
Calories burnt:  5771 (according to HR monitor, which knows my weight,  
age, altitude gained, avg. speed, an estimate of my VO2Max, max HR, etc.)

In terms of HR data, I spent almost 20% of my total time at or above 170  
bpm (91%+ of Max HR) and 50% of the time above 160 bpm (86%+ of Max HR).

Now, the HR monitor gives me 5771 calories burnt.  I have to say that I  
believe this number, as the ride I'm riding is nothing but hills and is  
absolutely brutal.  Nonetheless, even if it's wrong by half, it'd be 2885  
calories, and there's no way I took in that many calories for the entire  
day.

My impressions of the ride:  hellacious.  There are seven hills in the  
first 20 miles.  I stop at a local park, and I was shocked that I was so  
tired and still had 40+ miles to go (my goal was 70 miles, but I couldn't  
do that, particularly since it rained 80% of the time).  Then, there's a  
long climb up to a plunging descent (where I can hit 50+ mph in the dry),  
a respite of a relatively flat section, another long climb up to another  
plunging descent, then I turn around.  Those two plunging descents are now  
long, steep hills to be climbed.  (The benefit to the long climbs -- these  
are nice downhills; last year, I used to be able to haul butt down the  
long climbs, but the first 20 miles are so hard that I run out of energy  
now.)  On the way back to my house, I hit the two massive hills, then with  
2.5 or 3 miles from my house, I hit the "Col de Hogsback", which is an  
incredibly steep, short hill.  In about 1.1 miles, I climb 470 feet (8%  
grade?), but there is one very steep section, a less steep section, then  
another very steep section.  Yesterday, I again thought I'd have to walk  
up Hogsback, as I was bushed (and I put on a 12x25 rear cogset, from a  
12x27, so I now have harder gears).

Anyway, I have to say that I absolutely have to eat on my ride.  I also  
ate some amount of high carb the days leading to the long ride.  However,  
I was so tired at the end of the ride and immediately afterwards (I laid  
on the floor for about 20 minutes), that I cannot tell whether carb  
loading helped me or not.