The question of how to fuel one's self on the ITI route has been asked ad infinitum and will never be completely answered. The correct answer will always be some variation of "It depends", and the variables are you, your gut, your mental baggage, the ambient temps, what your goals are for the event, as well as relative windspeed when cross referenced with the angle of the dangle.
The correct response could be mistaken for the answer to the Omnivore's Dilemma: Eat food, not too much. But even that says nothing because we all define food differently and too much for me is a starvation diet for almost anyone else.
We all know someone, probably many someones, that swear by some variation of astronaut gels with barely pronounceable marketing-based names that taste like ass and eventually make you feel similarly. The people that eat this stuff swear that it gives them consistent energy for as long as they consume it.
And that right there is the catch: You have to eat whatever it is that you decide on for a long time -- maybe 3 days, maybe 7. Today is Sunday -- let's do a little mental exercise where we think back to what we had for breakfast last Tuesday. Was it a gel-based substance? Probably not, but even if it was, you didn't eat it for every meal of the last 6 days. Yet some athletes would have you believe this is the way. More power to them, I say, but I think life's too short for that.
So what should you eat?
My answer has been different every year that I've participated in this event, and would undoubtedly have morphed were I to line up again this year.
A not-atypical selection.
Here's how I do it:
First, I start with a clean slate, making no assumptions about what I might or mightn't want 3 days into the ITI. I know only that it has to be edible when frozen, needs to sit in a box in a warm post office (or en route) without spoiling for a ~week, and needs to be something my body can process when I'm working.
Then I go out for a long, hard weekend ride: something like 10 hours on the bike, usually finishing in the dark and well after dinnertime. I'll take not quite enough of whatever random snacks fall to hand, eat them as needed while riding, then on the way home, hungry enough to eat roadkill, I'll stop at a grocery store. Just my neighborhood grocery store. There I'll stroll the aisles and grab anything that looks remotely palatable and everything that my tired, depleted body is craving. When I do this exercise I usually plan to spend at least $100 and maybe twice that, never knowing for sure which delicacies will shake out in the end.
While shopping it's important to keep the three food groups in mind: Sweet, salt, and substance, reminding yourself to keep the proportions roughly equal as your cart begins to fill.
Basic examples that have made the list at various times through the years and that you'll always see being consumed during the race include pop tarts, cookies, crackers, chips, beef jerky, summer sausage, licorice, gummies, Cheez Whiz, cake frosting, cookie dough, chocolate bars, energy bars, M&M's, and sammiches of all sorts.
I'll sample casually from everything in the bag on the way home, as I put the bike away, while showering, after showering, right up til bedtime. The idea being to simulate what your body wants when depleted, then to wake up the next morning and see what still looks appetizing enough to eat. I'll continue grazing on any/all of it through that day and into the next, at which point I already have a pretty good idea of what my "tastes" are going to be.
One year I rode to McGrath eating PB&J burritos and not much else. Temps being what they were, the jelly had frozen and within it there were ice crystals that I was convinced were helping to keep me hydrated, in addition to the bonus caloric density of the peanut butter and tortillas.
The next year I took burritos but this time they were filled with Velveeta and bacon. A lot of bacon. 15 pounds of bacon. My house still smelled of bacon when I got back a month later. And I still get a quasi gag reflex thinking of the Velveeta. But that's what looked good in the store that night, and what continually tasted good in the weeks leading up to the ITI. And that was all that mattered.
Leaning in a very different direction, one year I ate four and a half pounds of Mike & Ike's en route to Nome, and stopped at a convenience store on the outskirts of that coastal village to grab another 8oz on the run in to the finish. I couldn't get enough of them, and felt invincible as long as I could hear them rattling around in a water bottle on my fork leg.
I've never worried too much about vitamins or supplements during the event, knowing that a balanced diet before and after will iron out any inconsistencies introduced during the speedbump that is the ~week of the race.
After drilling down to identify the things your body wants, you repeat the process on an overnight ride a ~week later, taking your finalists along to eat while riding, while bivying, and while riding some more the next day. The idea here is to test them and filter out the duds that looked appealing in the store -- like Sour Patch Kids or Crunch Berries -- but that weren't ideal because they shredded the inside of your mouth and left you with little interest in eating anything.
Perhaps the most important thing to remember is that you can never be sure what your body is going to want when out there. John Stamstad used to quip that (for a 24 hour race) he'd need something like $25 worth of food, but he never knew *which* $25, so he'd buy $100 and pick from it as needed. Taking someone else's list will almost never work, which is why I never supply lists. Experimenting on yourself in the weeks leading up to shipping your food drops is critical, and that's what Jeny's out doing right now.