Great job, @TofuguKanae ! That’s a great list.
I’ll definitely bring some list of foods that may consist nickel if it’s serious, cuz it’s a not common allergy. Actually, I’ll make a phone call or send an email to make sure if they can deal with that issue prior.
The card @alexbeldan alexbeldan posted seems to be fine too. If I use that card, I’d say,
I have metal allergy and can’t eat any foods containing nickel.
Although you have specific metal allergy, metal allergy is more common allergy that people are familiar with and I thought saying that word might help people understand better.
I’d also add,
Even though you use foods without nickel,
if they were cooked with stainless equipment, that would contain nickel and I can’t eat it.
50 yen, 100 yen, and 500 yen coins contain nickel too, so please use different coins for changes.