I am really not setting myself up as a PPP expert but one of the great things about the wonderful PPP organisation is that they carry drinks to R. and HI.
Practically one cannot take in too much energy during the race and not having to carry gels, drinks etc is a great help. I drank 4 small tetra-packs of apple juice, ate 3 gels and drank 1/2 litre of tomato juice from two plastic bottles. The latter is not high in calories but it is a fluid and contains salt and I think this offsets cramp. I had no cramp on the run down from I.