Eat something before you ride - don't worry about supplements on your bike for a 12 mile ride. Take water with you and some fig newtons for if you get lost or have a mechanical and happen to be out longer than you expected to be.

Things you might eat would be an english muffin with a small amount of peanut butter (yes it is high in fat and protein it will give you the energy you need). When you come home from your ride, eat some fruit, banana, peaches, whatever you have and make sure you drink.

Longer rides would require more food intake when you get back from your ride. Immediately after your ride is when you should try to replace food into your system. That is when your body will utilize it most correctly and you will recover well for the next day.

I don't take supplements with me unless I'm going for about 40 miles, then I will eat a gu. This is on a road bike, this changes when I am riding a hard mountain bike ride it is a shorter distance because the riding is harder and takes longer This is different for everyone tho. The more you have trained, the more you have ridden,the more your body becomes able to use less food. It becomes more efficient. I used to have to eat more.

Calories and output that is weightloss. If you burn so many calories, you can eat so much. If you up your calories burned, you can eat more. That is how a diet works - it is like a car engine. Food is just fuel.