For what its worth the following are what I tend to take with me on marathons before, during to keep me going till the end and after:
When it comes to gels, whilst I am blessed of having cast-iron guts and am able to deal with anything without feeling like I am about to honk, I prefer the smooth liquid gels that you can just slurp down rather than having to chew your way through with the sensation that your mouth is being glued together.
As well as gels, I also chew my way through slabs of jelly... Yes the blocks you get wrapped in plastic that you water-down to make children's desserts! They carry DOUBLE the punch of an energy gel by weight in both calories and carbohydrates at around half the price of a single gel. The one thing I will say is you do need to wash them down with a bit of water as you chew your way through as they can dry your mouth out a fair bit.
In an effort not to over-rely on gels/ jelly during runs and to eat something of substance as well - a good habit to get in to with my wish to step-up in to ultra distances in the future. To provide a good top-up to my energy I'm chomping my way through Kellogg's Nutri-Grain bars (or supermarket own brand equivalents) for sustenance during the runs, as there's nothing worse than having an empty stomach that feels like it is rubbing against itself.
I have also begun to use another High5 product to chomp on along the way in the form of their Berry flavour 'Energy Bar', which as time has seemed to have the effect of rocket-fuel for me!
During the race I run with a Camelbak bladder with around 2.5L of High5 Zero X-Treme electrolyte & stimulant drink in berry flavour. The tabs when you drop them in to the bladder effervesce until nothing remains, and the jiggling up and down of the backpack as you run certainly makes sure everything is well mixed! The drink is totally flat so there's no issue like you have with the carbonated energy drinks normally found canned and with the added essential salts contained within the mix it guards against cramp, something that I have mercifully been free of so far - except for the last mile of the Portsmouth marathon.
Before a race I tend to have a cup or two of black coffee and flapjacks, and for recovery after a race I drink a shaker of protein recovery shake.
The brand I am using at present is SiS REGO powder in strawberry flavour.
Which at least tastes like the flavour it is supposed to be, unlike others I have tried!
I also tend to chow-down post-race on a couple of 'scotch eggs' for a further protein blast - as let's face it you don't get more of a protein based snack than a boiled egg wrapped in sausage meat!
And last but not least, it would be rude not to mention a good pint of ale supped in celebration of chalking-off another marathon :)