I avoid coffee or any other diuretic as it is dehydrating and makes me want to pee.

As far as nutrition goes, I'm on a ketogenic diet (LCHF: Low Carb, High Fat) and the great thing about it is you don't need to worry about "carbo loading" or eating GU etc. I like to tell my fellow riders, I burning diesel (fat) you're burning gasoline (glucose.)

A nice breakfast like 10 wheels (minus the coffee for me) is all you need. And I don't worry about eating along the way. I won't need it. A good hard ride burns 800 - 1,000 cals an hr. Even the an athlete with 8% body fat has over 40,000 cals of fat available.

The down side is a ketogenic diet is very dehydrating so LOTS and LOTS of hydration and electrolytes are required.