You can approach this from another direction. Cycling 8 hours a day will (roughly) require about 4000 calories, although, as mentioned above, headwinds, hills etc. can increase this. Then add in the average daily maintenance requirement of about 2000 calories and that leaves you needing 6000 a day.
Hobbits know what this means. A good breakfast, something mid morning, lunch, afternoon tea (hey! I'm a Brit
and a good evening meal.
As a young soldier I was given a good tip about salt. Take a pinch of salt and taste it. If it doesn't taste salty, you need salt, otherwise you don't.