Hi Rosie, Best of luck on your 1st Ascent. This is one difficult race, for a lot of reasons, as you will see. Nutrition being one of them.
I post my reply mostly so you get some variety of answers.
This question was asked on the Message board not long before the race in 2014, I think, and when I replied the responses already ranged from 300cals in Gels to 2,600cals total- so whatever you're thinking for how long it will take you, and how much you might eat during that time, I bet you are correct.
In 2014 I said I took in 980 on-trail calories in the form of 460cals Liquid (which during the race would be in a 1 liter Race BackPack), 120cals early on, in the form of a pre-broken Bar (PowerBar at the time), and 400cals in Gels throughout. I also took in 4 Endurolyte Tabs that year, but I usually use Salt-Stick Tabs, and only used the much lesser-per-pill Endurolytes because my drink had ~1250mg of Sodium!
During this year's race, along with the 'water pack that has my liquid calories in it' I'll have a hand-held bottle to take on water at the 7 aid stations. I'll be wearing both a Cycling Jersey with Pockets, and Race-Ready shorts with Pockets. I'll have had about 1,000cals for Breakfast, and will take at least 5-6 Gels with me, and about 900cals in Liquid "Go Juice" in the Ratio 84% Carbs, 11% Protein, 5% Fat. And I'll have Salt Stick Tabs with me.
Best of Luck!