My favorite gel is PowerGel Strawberry-Banana. I can choke it down easier than the others. It seems like eating toothpaste but is very helpful on long rides for me without adding too many calories.
On shorter rides (40 miles or less) I usually like one rest stop to refuel quickly with a banana and some cold water. I can feel the point when my body is out of food and starts to use fat. I need to let that happen and ride past it because I have had trouble carrying too much weight in the past despite the fact that I ride over 4000 miles a year.