I'm usually okay with water for rides less than 90 minutes, though sometimes I need a snack after an hour or so.

For anything longer than that, I plan on 200-300 calories per hour. Some are from Gatorade while other calories are from snacks. I have trouble eating solid food when the weather is hot so I generally stick with carbohydrate gels and chews. I like Gu and Gu Roctane for gels and Jelly Belly Sports Beans.

Everyone is different in terms of what they like and what sits well while they're exercising. In general you want something that digests quickly and easily.

I've gotten lots of useful information about what and how much to eat before, during and after long rides from Nancy Clark's Sports Nutrition Guide Book.