I recently returned from a trip to Florida on British Airways. On both flights there was an announcement that some passengers have a severe nut allergy and so we were instructed not to eat food containing nuts. I know that small traces of nuts on surfaces can be a problem, and I've read reports of air-borne traces causing reactions. For the purpose of this question assume that this is indeed the case, the air-crew have instructed me, and I want to comply with the letter and spirit of the request.
My usual practice for a trans-Atlantic flight is to buy a small snack to be consumed if I don't like the supplied meals. I often also bring a "Snickers" or "Payday", both containing peanuts, and in the latter case those nuts are on the exterior of the snack.
Hence, playing safe, I keep the Snickers and Payday in my bag, I'm complying, no nuts.
But the sandwich? One sometimes sees notices such as
This product is prepared in a kitchen where nuts are used. It may contain traces of nuts.
Assume that I want to do the right thing, how do I determine whether to open the sandwich? My instinct is that a simple ham sandwich in white bread simply cannot be a problem, but am I right? So, ask the flight crew? Do they know? Do they have training?
I see from this article that issue is quite tricky. My proposed course of action is to ensure that I don't bring sandwiches explicitly containing nuts (eg. cashew chicken wrap) but feel free to eat anything whose ingredient label does not specify nuts.