On low intensity training rides up to 3 hours I eat very little (or not at all) and often just drink water. On higher intensity rides up to 3 hours I fuel with liquid carbs, gels and bars. But not many. Maybe a couple of bars, a bottle of carb mix and the odd gel.
On competitive events much longer than 3 hours I consume as many carbs as I can comfortably tolerate throughout the event, which is about 1 bar + 2 gels + 0.5L of carb mix per hour. As the hours tick by, I find it harder and harder to take in solid food and resort more to carbs in liquid or gel form. The longest events I do like this are under 10 hours and I don't ride anything longer. I can take in approx 80g of carbs per hour in this mode. I know pros can and do tolerate a lot more. I also know it takes training to increase your tolerance to carb intake on the go, but I don't push that too far as I doubt it's particularly healthy.
If I'm racing flat out on Zwift for an hour or two I will also fire down a couple of gels and a bottle of energy mix. I find it just makes it easier to keep putting out the repeated efforts required without fading badly at the end.