If you think about it, you probably burn 300-500 calories per hour -- some more some less, when riding. So, if you eat/drink say 250 calories an hour you should not go hypoglycemic.

Go for a sports drink that has plenty of carbs and electrolytes and then a carb replacement like Power Gels, GU, Clif Shot Blocks, etc. If your stomach can tolerate it, you may want a small amount of protein if you are out there over two hours. Personally, I can only tolerate Clif Shot Blocks and Cytomax sports drinks... I've tried many other, but my tummy says "no".

It's a trial an error, but you have to eat an awful lot on the bike to gain weight!! Just be careful to eat reasonably when you are off the bike. There are some that say that within 45 minutes of ending the ride you should have a snack that is 75% carbs/25% protein. Something like low-fat chocolate milk and a banana.