Can't figure out foods (need guesses to test)

[ThisIsMyUserName]

So I'm not celiac, but have severe food intolerances and this board has been extremely helpful in helping me figure out my intolerances. I know for certain that my main culprits are caffeine and dairy. When I stopped those I went from throwing up daily and being nearly bed-ridden to being generally functional with some incidents. I have been doing this (with detailed data and spreadsheets) so I know for sure that certain foods repeatedly cause me to have horrible reactions, but I can't figure out what the problem is. I know, without a doubt (multiple tests), that I can have gluten, corn, and soy, so it's not the usual hidden things. I am listing the foods below that cause me problems, but I can't find any underlying theme or culprit (for example, most of these have gluten, but I can eat entire loafs of bread and bowls of barley and be fine). I've looked for common ingredients and can't find anything that jumps out. Would people be so kind as to propose what might be the problem? I can live just avoiding these foods (and adding to the list as necessary), but I'd be much happier if I knew what the underlying issue is so i can comprehensively avoid it. I've never had a problem with any whole foods. Thanks!

The list: all breakfast cereals (including chex and gluten-free cheerios), pretzels, fresh breads (at least from the breadsmith near me; I can eat packaged breads), trader joe's crumpets, some deli meats (others are fine). Help?

[squirmingitch]

Look for some preservative that is common to all of those items.

[stri8ed]

Maybe Histamine Intolerance?