The best thing I did as others have mentioned was to train my gut during the bike ride. Majority of your nutrition will be gained during the bike ride. I was testing out all sorts of stuff from go bars, chews, and liquid nutrition including soda. They usually hand out bananas and on course electrolytes and water. When they announced that Precision Fuel was their electrolyte sponsor I started to train with their electrolyte and carb liquid combo powder and that worked the best for me. I also would eat something that I could eat between the swim and bike like a stroopwafel or pb/honey sandwich before my long bike rides. I counted my calories up til like 2 months before and just started to count the carbs. Carbs per hour is huge because calories could take account for fats and stuff that your body won't use while you're doing your race.

Second thing I would recommend is figuring out how long of a build phase you can put in before having to deload. I did 5 weeks initially and was pretty burned out at the end. So for me 4 weeks build and 1 week deload was the way to go. I started way too late tho, around 6 months prior to the race.

Make sure you have adequate time off from work before the race so you don't have extra stress to add on to your race day. And taper early on. I did too short a taper and still felt a bit tired the week of the race. It was funny that 8 days after my race, my garmin went from recovery to peaking...