Breakfast: (3 hours before start)
Oatmeal, banana and bottle of Powerbar Perform (I like the added electrolytes especially at a hot race).
I'm planning to try rice cereal before my next race.
Pre-Swim: (20 minutes before start)
One Double Latte Gel
Bike: (I eat every 20 minutes)
Basically I alternate between swigs off a bottle I have filled with 14 PowerBar Gels + water, and half a PowerBar (I used smoothie & Peanut Butter in TX) at the top of each hour. Over the course of the ride I end up going through the entire bottle of gels and two full PowerBars. I drink water and Perform on course (in Texas I drank a LOT seeing as it was hot). I don't worry about taking salts because the PowerBar Energy Gels I use have a good amount of salt in them.
Due to riding a bit harder along with my small bike implosion around mile 85, I ran out of gel and ended up grabbing one on course. My next race will have 15 gels in my bottle.
A note on caffeine:Caffeine works wonders - when you are feeling slow it gives you wings. For me it can also make me feel horrible if I have too much of it too early in an Ironman. (Kind of like I have the flu). Therefore I don't use much caffeine on the bike at all and save it for the run. My bottle of Gels on the bike contain mostly Vanilla or Raspberry Cream because those do not have caffeine in them. I've learned this mostly through trial and error. I have friends that use tons of caffeine from the gate. My advice is to test what you want to do on race day in training.
Run: (About every 3 miles)
The run is gel, water and coke for me. I alternate between Green Apple Gel (my favorite when running) and Double Latte on the run. I don't exactly have a science to it - other than I leave T2 with 4 gels, pick up another 3 at special needs, and almost always have one in my hand. I try not to take cola until the half way point, but usually end up grabbing it much sooner. If I end up feeling overly hungry on the run I'll occasionally eat part of a banana.
The above is practiced on multiple training rides during the year. My long rides with hard efforts all are done with PowerBar gels in a bottle, just like on race day. There tend to be less surprises on race day when I have spent the entire year training with the exact same nutrition.
Hope this helps a bit when planning out what you will consume during your day-long race buffet! Feel free to email me with any specific questions.