Or you could type up "My allergies are X, Y, Z, I have the following preferences..." etc. and put it into whatever chat bot you like. Obviously this is a bit of a pain, but it probably constrains significantly how much of a premium ChatGPT can charge. You might not bother if ChatGPT is time and a half more expensive, but what if it's 3x as much as the competition? What if there's a free alternative that's just as good?
I pay for the $200/mo ChatGPT, to me that's insanely cheap compared to the value it provides. Better pricing is highly unlikely to make me switch. If a competitor were able to sustain a lead in model intelligence/capability then I'd consider it.
Even simpler, ask ChatGPT "How would you describe my dietary preferences and restrictions?", maybe throw in some personality guidance of "You are training my executive assistant".