Boiled or poached eggs or porridge with blueberries for breakfast. Sometimes I have toast or cereal.
*A note on "other food". By this, I'm referring to the necessity to have a roof over your head and the basics covered during the period you want to write your novel. You may decide to do this over a long period (like, a year) and fit it into your normal routine. You may have a vacation between school or college semesters. You may decide to stay with friends or family and write your novel intensely over that period... if you are invited! You may still be living at home or in a place of your own... the point is, adapt to whatever your circumstances allow. Just make sure you have the roof, food and funds part covered (and the desk, chair and space.) It is a noble thing to work during the day and scribble by night. It is also great if you have your old room available to you to hide out for a month or two and get that novel draft done! But only if the peeps around you are supportive. If they are not, and you are old enough you don't need me to tell you it might be best to get a job, keep a job and write when you get the chance to do so. Better yet, if you have some funds set aside, give yourself a space to work on that novel, then you get to move back to normality when your writing is done. There is no metaphorical 'statute of limitations' on creativity. Some people take a year to get that draft done, some take a month. I believe, some, have done it in a week.... every person is going to be different.
But getting back to reality...
Once you've got your smoothie (which counts as both your food and drink should you want to work through - though I'd advise getting up and stretching when you need to!), you should sit at your desk in your comfy chair and take a piece of paper and jot down your ideas. Your first ideas for your novel. Go to it, Lovelies! Tap into your creative energy. The sky is the limit - at first. If you like to draw, why not sketch some images also? You may draw a house or a character or the clothes they wear. It all adds up to an idea - who knows you might like to try a graphic novel one day (or straight up!) I hear they are hot, hot, hot.