I finished my first 600k in July so I'm not exactly an expert. Since I don't really ever get hungry and don't like to eat a lot of solid food on long rides, I made sure to get enough calories. I pre-measured a bunch of 300 calorie servings of bike food in ziploc bags (powdered maltodextrin and whey protein that I mixed with water) which accounted for around half of my calories. The rest I got from small-easy to digest food from the controls. The last 200 I didn't eat any solid food at all, just the bike food, juice and sports drink. I rode the first 400 in around 20 hours, slept for four hours in the back of my minivan and finished the last 200 in another 10 hours. I originally planned to finish without sleeping, but changed my plans after completing the first 400.