I had less breakfast than usual before the GNR, my sister had more than usual (we each had a pot of thick and creamy yogurt and a croissant and jam with coffee), but she was the one who ran out of steam at ten miles and was lying in the aisle of the bus with hypoglycaemia afterwards. Must admit, I felt starving while we were hanging around waiting for the race to begin, but that had settled by about 6 miles.
I think it has a lot to do with training and, in particular, developing the ability to use fat as fuel before running out of glycogen. It probably helped that I don't think I ever got out of my aerobic heart rate range.
People ran races, and ran them well, long before gels and bars and Lucozade Sport were invented. I'd much rather forget the sweet gunk and be like John Bingham and stop for a cup of coffee mid-marathon if the opportunity presents itself.