If you banned every food that people are potentially allergic to, then quite frankly there'd be nothing left - especially when combined with other dietary and practical requirements. I once worked with someone who had an allergy to oranges and banned them from the office; it really can be any food. 

The combination of requirements is especially acute on flight where you've got to factor in 

• any allergies other passengers might have (even if we just assume the top 14 allergens, that's hugely restrictive) 

• the liquid ban on flights - so no juices, hummus, yogurts, huel shakes etc

• the total lack of access to cooking facilities 

• you have no way to keep food safe and cool on a long haul flight - ice packs are banned under the rules on liquids 

• you can't take knives, so no cutting up fresh raw fruit or veg. 

• other dietary requirements - for example I'm a vegetarian. I have tried ordering vegetarian meals on flights, and even when you have written proof you ordered them, it's hit and miss whether or not they'll turn up (50% success rate on my last 4 long haul flights) so you have no choice but to bring your own food as backup. 

Anyway, if you can suggest food that's vegetarian, 14 allergen free, doesn't require heating or refrigeration, isn't liquid and will be allowed onto a flight, and is substantial enough to sustain me for an 18 hour flight (crisps won't cut it) then I'd love to hear it because I'm flying to SE Asia later this year. 

I've asked this before on such threads, and what I always receive is a load of hot air (I usually get called selfish) and not one sensible suggestion for food that actually fits all the criteria imposed on us while flying.