I'm VERY picky, and can eat the same thing every day forever, and I'm happy that way. However, to be practical, I do go with the flow, so to speak, and will be flexible when going out to dinner or when other people are involved. Otherwise, I've been eating the exact same thing, same portions, for breakfast for many years, 365 days (or 366 on leap years).
I'm lucky that the things I really hate in food, are fats and sticky/slimy things. I can't stand anything with mayonnaise (looks like horse semen to me), and I can't stomach anything deep-fried. The smell of frying or cooking oil is repulsive to me. I say I'm lucky for all this, because it's easy for me to eat a healthy diet all the time without discipline. I am in no way enticed by french fries or salad dressings, nor sticky cake, or other stuff that most other people say they crave.
When I eat lunch out, I have been going to the same style of place; Mexican or Tex-Mex. I get flame grilled chicken or steak tacos or burritos with no guacamole or anything else slimy. No cheese. Just steak/chicken and BLAZINGLY CORROSIVELY HOT salsa. And water to drink. (Coke makes me thirstier than before I drank anything). I've been going regularly to the same take-out place for so long, that the cashier was a teen when I first went there, and now HER daughter is going to have a baby! They originally had 3 locations in the Los Angeles area, but now only have one left which is 40 miles away. I still go there at least twice a week, and more often as logistically possible!
Charles