I wrote up some thoughts for my friend Emily that might be useful to post here.
I promised some pre-race & race day fueling ideas. These are from Joel Friel's Paleo Diet for Athletes, and what I learned from Jeff Galloway. Also Dean Karnases' 50 Marathons in 50 Days (insane, but he did them). He has a free download from his audio book.
Take a look at Dean's three-day countdown. I would emphasize drinking a lot of water during the days leading up to the race. It will help your body store more glycogen and your muscles will work better. There's only so much you can absorb the morning of the race without ending up with a full bladder and no pot.
When you wake up on race morning: right away, drink 700 ml water and eat 150 calories of carbs (pre-race fueling); then eat 200-300 calories per hour up until an hour before the race: mostly carbs (no dairy) (the longer before the race, the lower glycemic load - in other words, don't crash!). Examples of what to eat: low fiber; high Branch-Chain Amino Acids (egg whites; protein powder with applesauce) - (jarred baby food) Bananas. Not berries (too much fiber). Drink water. Some people like to eat meal replacements like Ensure. (groan).
In the last hour: drink only water. No more food.
10 minutes before the start: high glycemic fluid - 100-200 calories of sports drink/juice/honey water or water + go-gel.
During the race: It depends on the duration of the race: under 90 minutes: goal is to prevent dehydration: 4 oz water per 10 minutes. Avoid solids & gels. @ 1 hour: maybe a carb drink. Research is contradictory.
**edited to add: this number seems too high. I'll have to go back and check. I've read often that the point is to drink enough to replenish water lost through sweat, but to not gain weight during the event. So, weigh yourself before & after training runs under race-like conditions to see how much you sweat. I never tried this, but it seems like a good idea.
90 min - 4 hours: 800 ml fluid per hour. If maximum intensity: 200-300 cal/hour, divided into equal doses every 10-20 minutes. At least 1 calorie per pound of body weight per hour. This means 50-75 calories every 15 minutes. If Gel = 100 cal + 8 oz water. Some say that products like accelerade, which mixes protein into the carbs, work better. I've found similar kinds of mixes here. So for me: 1100 calories to eat during a 5.5 hour race.
After the race - recharge within 30 minutes - makes recovery easier. I usually eat a smoothie (carb & protein mix). I have a recipe for this, but I can't find it in my training journal. Holler if you want this too.
I have to admit, after 4 -5 gel packs, I want to puke. And during the marathon I felt slightly sick to my stomach from trying to consume enough to fuel my effort. During my training runs, I was happy to eat bananas, dates, and stuff like that. I did not want anything in my stomach during races, though. I switched to apple juice and sweetened black tea.
Always - this advice depends on your body, not mine. You might process fuel faster, sweat more, sweat less, whatever. See how it goes.
And be sure look at the recommendations of how much fluid to drink during a long race. Not too much and not too little.
Wishing you success!