You don't need that many calories. 3000 calories would be more than 400 calories per hour, which is way more than most people could keep down. 200-250/hour is more realistic. You don't need to replace calories as you go anyway; that is what body fat is for.
I like to make PB & J sandwiches and cut them up into quarters. Maybe a couple of those, some gels if you're into that kind of thing, and some gatorade-type whatever. That should cover it.