I do, because that's what my doctors recommended. I take Benadryl and wear a mask since the flight sometimes serves shellfish too. I also wear a jacket and long pants and a mask that filters particulates. The only trouble with the mask is that I got really thirsty 

Like ra3chel, I take it as well, but again, am an adult.  I tend to have just as many, if not more, problems with non-food allergens on planes, like pets, people with pet dander on them, perfumes, etc., so it makes sense for me.

I do, BUT:

-I'm an adult. I know my own reaction patterns, I don't have to worry about sticking my hands in my mouth or eyes, and I'm very careful when I travel.

-I only fly on airlines that don't serve peanuts, and I ask my seatmates to be careful about what they open before the flight takes off. I've never had anyone be less than civil about this.

-I always pre-board and am extraordinarily careful about things like wiping down seats and surfaces.

-The symptoms that have been issues for me on planes are almost always cutaneous--so, things benadryl does help with. I also find flying badly nauseating; for some reason, the thing that counters that most effectively is a combination of benadryl and muscle relaxants (yes, I have my doctor's blessing for this; yes, I'm careful).

I wouldn`t either.  I don`t want to be late in recognizing a reaction.   I would just be super careful about what he eats, bring all of his food, and if he is only pa, and they do not serve peanuts, he should be fine.

Personally, I wouldn't.

This is a situation in which you will need every bit of time to recognize what-- exactly what-- you are dealing with if you have a problem.

Benadryl won't mask anaphylaxis anyway-- and it can remove the built-in "early warning" system in kids which high sensitivity, because it may make them less aware of discomfort with their surroundings because of the sleepiness that it can cause.

Can you give a non-sedating antihistamine instead?  That does a nice job dampening irritating symptoms without causing CNS effects.

What does your allergist think about this one? 

I was just curious about what others do before boarding a plane.  There are no peanuts to be served, but there is a "may contain" on one of the snacks.  There *might* be roasted tree nuts in first class. (We are in coach and he is allergic to peanuts only.)  I have heard that some people give Benedryl before the flight, but then others say it might mask symptoms.  What does your family do (or would do in our case)?