your body holds enough glycogen in storage for you to run, at marathon pace, for around 2 hours, without the need for supplementary fuel.
your body contains sufficient fat in storage to fuel running at slightly slower than marathon pace for TWO DAYS without the need to refuel.
if you are suffering from anything on your long runs then it has absolutely NOTHING to do with fuel availability or whether you had 37 grams of honey on your cheerios forty seven minutes before your run. that is just gibberish given to you by folks who want to sell you something.
what you might be needing on those long runs is water. just plain old water. tap water. you don't need Doctor Gruel's special sauce with microbytes and fuel enzymes or what-have-you. just drink water.
after you have been running for around 45-minutes or so, your digestive system (and other non-essential systems) effectively closes down so as to limit oxygen consumption and divert blood supply to the cardio-vascular system and the skeletal muscles. at this point, anything you ate before your run is just junk in your gut that serves you no purpose whatsoever. it's just excess weight for you to carry.
the bonk you are feeling, is, essentially, in your head. you can flush it out by drinking water, and reading a good book on how your body actually works.