Everyone and every ride is different. It's hilly here, and I do some rides hard, some moderate. Short rides, say up to 50 miles, I'll take a bottle or two of HEED and won't necessarily drink at all at the short end or finish the two bottles at the long end, which total 300 Cal.
When the rides get longer and harder, I'd run out of glycogen if I didn't fuel properly. For those I mix a powder of 7 parts maltodextrin to 1 part chocolate whey protein, by weight. 2 cups of that in a 24 oz. or 1 liter bottle is 750 calories, or 3 hours of riding strong. Since these rides will be more than 3 hours, I bring extra powder in Ziplocs in my saddle bag. I've mostly given up on solid foods. It's just too hard to digest when I might be climbing in the heat for a couple hours at a time.
I buy the malto at a homebrew supply house in 50# bags and the whey online in 5# containers. I go through about 1 bag of malto per year, costs maybe $80. On really long rides, I can't carry enough powder, so I'll eat whatever along the way, fruit pies being a favorite. But on really long rides, effort is low enough that digestion isn't that difficult.
Main thing is to keep the carbs coming a little at a time, no long breaks between fueling. Back when I used to use Clif bars for fuel, I'd break them into quarters and eat a quarter every 15'. That works OK, but I prefer liquid now, same principle, drink a little every 15'.
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