it's best to not ride on a completely empty stomach (early AM rides). Just eat what you'd normally eat for breakfast, ideally an hour before you start but I can eat and ride immediately. What works best for me is pancakes and eggs for a pre-ride meal in the AM. Whatever you eat, just make sure it always agrees with you, don't go experimenting with foods you have not tried before rides before. Later in the day I make sure I just avoid the spicy stuff......salsa, jalapenos, onions etc and stuff that might cause you indigestion (cucumbers does that to me). And also make sure you just eat normal portions and don't overeat.

I've done tours where they feed you on the ride and I've never had any issues with eating and riding myself. but when in doubt go bland.