As a high school swimmer I really struggled with this (and I was swimming 4.5hrs a day, so not eating was not a good option).
I found protein shakes (especially ones made with almond or other non-dairy milk) to be fairly easy to eat; and I would use those as a breakfast most of the time.
Another thing that helped me a lot at all day meets was just letting myself relax about food, and not try so hard to eat as much “proper” food as everyone else was.
For me, I felt sick because I was anxious, and trying to force myself to eat was just adding to my anxiety. I switched from worrying about getting “enough” calories, to finding foods I could eat at all, and allowed myself to just have a bite here or there all day. Lots of small snacks (like a few bites or less) was the key for me, and then I slowly started being able to eat larger snacks because I wasn’t making myself feel worse every time I ate!
Simple sugars are helpful, and your body is probably not that efficient at metabolizing proteins when under stress anyways.
My favorites were grapes, clementines, goldfish or oyster crackers, chocolate milk or lighter protein shakes, and Gu energy gels and gummies.
For me, it was really important that I could have foods right in front of me, and that I could eat in very small amounts. The smaller portions didn’t bother my stomach, and if I ate lots of small portions, I never felt that bad by the end of the day (still tired, but not exhausted/hangry). Just a few grapes or crackers would keep my blood sugar up, and help my body metabolize pre-existing energy stores effectively.
My new favorite nervous-stomach foods are the lemon luna bars (citrus doesn’t make me feel as sick as other flavors), and Bel-vita breakfast biscuits, those are very crackery in texture, so I find them easier than granola bars.
