I usually do a gel every 30-45 minutes and sip the sports drink throughout. I try to drink at least a bottle of sports drink or water between aid stations (so that's about a bottle every 10 miles). Like said above, it also depends on the conditions for the day.

If it's a HIM, I only do gels and sports drinks, and then take a salt tablet every hour or so. I lose a lot of salt, so I try to replenish it often. I don't do solid foods for a HIM distance or less - my stomach doesn't like it coming off the bike that soon into the run. But again, keep experimenting and play around with it in your training. That's the only way you'll really know what works well for you.

Another thought: Make sure you do some 30-60 min runs after your long bike. This will tell you if you are dialing in your nutrition properly.
Sometimes you can feel great on the bike and then the stomach can rebel on you a bit when doing the run immediately after the bike (usually when you don't hydrate properly on the bike). Just something to be aware of.

My best mates girlfriend is a dietician who specialises in sports nutrtion. The best thing I ever did was talk to her. One of the stupidist things I ever did was talking to her after my first IM where I did stupid nutrition things and hurt myself because of it. The following summarises my approach which is based on some very good evidence she supplied. I have used this pretty much religiously since and tweak it slightly depending on conditions. A little lengthy but I think it works, My tri mates use a similar strategy

1) Training your body to take on nutrition is as important as training for any of the components. You cannot perform if you are hypoglycaemic or dehydrated no matter how fit you are. It took me months to get up to tolerating the nutrition load I use comfortably and I tested complete nutrition plans on my long endurance saturdays several times.

2) You can absorb about 1g of glucose/kg body weight/hr so for me at about 75kg, 75g of carb every hour. I work in grams rather then KJ, most foods have both on the label

3) You need about 750mL of fluid per hour again for a 75kg male. In cooler conditions you can get away with less, in hotter conditions you may need closer to a litre/hr amybe more. Slightly over doing it usually means peeing more, however people have pushed themselves to coma by taking way to much free water.

4) Your body will alter concentrations of glucose/salt you eat to be the same concentration as your bloodstream. So if you eat a high concentration load without enough fluid your gut will secrete fluid to make it the same concentration BEFORE absorption. ie you can effectively lose water if you eat too much sugar without fluid. The first organ to shut down during dehydration is your gut, this is the main cause of those terrible gut cramps which hit people mid marathon.

5) Continual steady supply wins the race. Your ability to absorb glucose falls usually at about the 5-6 hour mark. Thus I believe you have to take advantage of the ride to keep the intake at maximum level before the marathon. Obviously not so important for half IM.

My overall eating plan:

-Breakfast 3 hours before race
-Gel 5 min prior to swim (27g) with 250mls electrolyte (Horleys replace)
-Gel out of water with another 250 mls thru transition
-750 mls of electrolyte per hour on the bike (Again I use Horleys but there are a million drinks this is about 1/3 of the calories) On the hour and 30 min marks I take half a gel (1/3 calories) and on the 15 and 45 min marks I take a quarter of a power bar. (1/3 calories)
-run I aim for 750mls of electrolyte per hour, I divide this by the stations and hit a gel or power bar only on the 30 mion and hour marks. usually I wind up a little fluid down

This reads as pretty a-retentive but talk to the pros out there and they put a lot of effort into this. I only use bars and gels on long training and racing as they are expensive, the important thing is teaching your body to cope with whatever you use and maintaing discipline to keep fuel going in regularly.

Jacmun: Great write up, I really appreciate the time that went into preparing that post.

I would add that you shouldn't forget to supplement yourself with additional salt. Sports drinks and gels don't neccessarily include all that you need. Determining what you need is best accomplished over time. I've linked to an article on my blog, but the link is broken now. Here is an excerpt that addresses my point:

This article can be found here

This is directed at those in hot weather conditions, but from my experience in the military, fluid loss and repelenishment are just as important in cold weather. So check it out no matter the climate you are training in.

To determine how much salt you need you just have to play with it. I know, sucks huh?

Some people I know take tons of extra salt in longer races, and I find what is in the Gatorade Endurance is plenty for me. I also don't train with salt supplements.

How do you know if you don't have enough salt, or too much salt? Are there warning signs that i need more salt or that i have too much or that I am just right?

Be careful with this. While cramping CAN be caused by low electrolytes there are many other potential culprits. If it were as simple as low sodium, why wouldn't our non-working muscles cramp? And why might a person cramp in a very short race (1 hr early season duathlon, for example) when electrolyte depletion didn't have enought time to set in? While the accepted explanation by most at one time, a better understanding of the cause of exercise induced muscle cramping is evolving. Good article here you might want to consider..

http://www.cptips.com/muspain.htm

Re too much electrolyte intake: since sodium (the most crucial electrolyte) draws water, symtoms of excess intake will be water retention related: puffy hands and feet, puffiness under the eyes. While generally not an immediate health concern, it will hinder your performance.