400 kcal per hour is the max most people can absorb.
I prefer 'normal' foods like flapjack and sweets, gels just give me stomach cramp and taste nasty.
Make-up some flapjack to this recipie
enough veg oil to cover the base of a very big pan (40g ish)
250g oats
150g chopped dried fruit (stick it in a blender with a dash of water to mash it itno tiny bits)
3tbs syrup
sugar if you want it extra sweet.
warm the oil (not hot or it will turn to a horible treakle mess) and sugar and syrup, stir to a paste and stir in the oats, transfer to rectangular cake tin should eb about 3/4" and bake at 150-160degC for 30-40min.
A mars bar sized chunk is arround 250kcal, so 4x half mars bar sized lumps per lap and your laughing. Start eating 2 bits an hour about 2 hours before the start to boost sugar levels for the inevitable first lap exuberance.