First question, did your previous plan work? If so (and you can remember it) why change.

There may be some general guidelines for a plan, but a nutrition plan is very individualized and only with trying it will you find if it works or not. I could say consume 300 calories per hour, but that could be way too much for you and way too little for the person next to you.

Figure out what products will be on the course and practice with those. If they work for you, great., Then you can rely more on the aid stations rather than filling your bike with stuff. If the products that are supplied don't work, find stuff that does work..

Find a route that is comparable in distance and terrain to your race and then dial in your nutrition at race pace.

Nutrition plan is pretty personal.
What I did ( only did two 70.3 ) was:

drink before the swim ( drink before the race, because you can't drink during the swim..well you can, but lake/ocean doesn't taste all that good) get on the bike and take some sips on the first few K's. Your body needs to adjust to go from swimming to biking.

Then on the bike drink every 15min and use half a gel every 30min. Gel I usually took with water and drink Gatorade when not using a gel.

On the run I didn't eat anymore, I had a gel while in T2 and drank water along with it. During the run I drank Gatorade and water at aid stations. When they had orange-slices I took those too.
Ow and Coke, when you start drinking Coke; DON'T STOP until you cross the finishline. Make sure to drink water along with the coke ( to prevent excess loss of fluids)

Just my 2 cents

I also tend to cramp alot, especially after 2.5 hours. During a marathon I take 5 gels. During last year's HIM a followed the basically the same plan Noel wrote about except I substituted gels for orange slices on the run.

Last year the Philly Endurasport had 4 total aid stations on the run and 2 on the bike. Plan to bring your own nutrition.

In a 1/2 IM, most folks will do just fine taking in 200 cal./hour on the bike, and then whatever you can tolerate (up to 30% of calories burned per hour) on the run.

You don't need as much in a 1/2 as a full because a) you are going harder and your body can't process as much intake and b) you're out there for less time, so if you take in a little less you generally won't have time for it to screw up your race.

That being said, it is still CRITICAL to have your glycogen stores topped off before you even start the race. Day before you should eat your normal taper meal, since you are working out less, and your body doesn't need any "extra" calories. Morning of race, I like to have about 600 calories in me before I start. I get about 250 from my preferred breakfast bar, and the remainder from Ultrafuel, and all calories (except for a few sips of Gatorade or even Mt. Dew!) are in me 3 hours before the gun.

If you're subjected to a delay of game, though (lake is fogged in, lightning, etc.), be sure to have easy-to-digest calories available, like extra Gatorade or Infinit or CarboPro or something like that, because once those 600 calories or so are in you, you only have about 3 hours before your body needs to start replenishing.

FYI, I use the same protocol before a marathon.

For a 1/2 marathon, I only need about 400 calories in the tank before I start.

For an IM, I go to about 800-900 calories in me before the gun.

For reference sake, I weigh about 112 lbs. Larger people may want a bit more in their tanks.

In training, whenever I am going to ride 4+ hours, I also dump in 600 calories before I start, but I can finish the intake a little closer to ride time, because it's not a race situation and I know what I can tolerate. When I'm going to run 2+ hours, as long as I do it first thing in the morning, I'm good with about 250 calories in the tank and then I begin taking in calories right away during the run (about 200/hour).

One of the nice things about having a full tank before you start is that you aren't looking to eat the entire menu of Chili's after your workout is done. You gave your body what it needed when it needed it, and so you will make better post-workout nutritional choices.

In many cases, IMO, people who have bonking (or near-bonking) troubles in 1/2 marathon to IM races weren't a victim so much of in-race nutrition errors, but rather they were starting on a less-than-full tank to begin with. When you do that, your body just can't catch up, because you are moving, which limits the calories you can take in.

The pre-race stuff is easily practiced during a race rehearsal brick.

When you have a full tank before the gun goes off, then you can apply the "less is more" philosophy of refueling as you race. Your gut will tell you if you are at the right level of intake. But if you're running on empty when you begin, then no amount of effort to make up the calories is going to work unless you stand down for a bit.