I define writer fuel as the food or drink you must have to get the brain going. You can do other things, such as take a shower, to get the synapses moving, but the fuel is needed to maintain the energy.
Here is my favorite, inspired by the coffee shops.
Poor Man's Mocha (or the damn shop is closed)
1 cup of skim milk.
1 tbsp baking cocoa powder
2 packets of splenda (or sugar what ever you like)
1 shot of espresso.
Heat the milk in the microwave in a tall coffee cup. Mix in the cocoa and the sweetener. If you mix fast enough with the spoon you get some nice foam. Top with the shot of espresso.
In case you are wondering. I don't have an expensive espresso machine. I have a espresso pot. They are also called a moka. You can pick one up for under $20. I got mine in Italy ages ago. Northwestern Wisconsin at that time did not have much in the way of "fancy" coffee shops. So when I had the change to go to Italy I picked one up, just to have. Now you can get them at Target, Walmart, pretty much anywhere.
So what is your fuel? What can keep you at the keyboard for hours?