I'm going to chime in and tell you what worked for me. I got third Expert Ironman in the V to R in '06.
I rolled up to the starting line prepared to just spend a long day out riding at my own pace having fun with a few buddies...er...a whole LOT of buddies.
I was prepared for the physical AND mental aspect of the race by training and riding just like you appear to be but I also felt that I may need a mental edge. So, I played a little game with the odometer on the XR 650R I was riding. The odometer only reads to 99 miles and then turns over to zero. Knowing this, let's say that the distance between pit 6 and pit 8 is 65 miles. If you roll the odometer to 35 miles at pit 6, you should be at 0 miles on the odometer when you hit pit 8. Mentally, it was a big deal for me because, the closer the odometer climbed to 100 (or 0) miles, the closer I was to friends,food and fuel. I prepared for this by adding notes to the pit crew notes so that someone in my pit crew (my brother) would know what mileage to roll the odometer to at each pit. It worked like a charm, especially when I ran out of gas. Had I not been carrying a little extra fuel in my backpack, a quick check of the odometer would have told me that I was only a mile from pit 13 and I could literally have pushed the bike there.
I had two camelbacks and I would make sure that my pit crew always had one ready to go with cold water if I was running low. In Nevada in August, the humidity is pretty low and you've got to constantly be drinking water. If you get thirsty, you're already dehydrated.
The same can be said for food. If you get hungry, the time to eat something is already past. I put my girlfriend in charge of food and she made sure that the food was already cut up in small bites and of a good variety. Some banana bites to combat cramping, some sandwich bites that included deli meats, bread, lettuce, and cheese, and some small fruites. She presented these items to me at each pit and I grabbed what looked good...but made sure that I didn't take too much. I didn't want to get bloated by the combination of the bread and the water I was drinking.
Of course, it helps to have your own pit crew for this sort of stuff. In the Ironman class, I knew that I was going to be riding slow enough for a single chase vehicle and, had they not stopped at a grocery store for lunch (a drive-thru would have been better), I would not have beaten them to pit 15 where I got gas from another team and headed to the finish line. In a team with fresh riders, we'll need two chase trucks to leap-frog the pits.
Then, above all else, I made sure that I was having a good time.
This all worked really well but I still finished the race 10 lbs lighter than I started. So, in my mind, it's definitely possible to be too skinny and without enough reserves.
I wish you the best of luck. Maybe I'll see you there as I'm hoping to be in a three-man team running open expert this year.
08 KTM 320 SXF, '07 Beta Rev 3,
Frankenberg 501, '96 Husaberg FC600, '68 Yamaha DT1, '74 Bultaco Alpina 250, '84 Husqvarna WR400 - My Dad says I've never seen a motorcycle I didn't want to own...