Same issues as going anywhere else - except you still can't carry your own water onboard. :)

Make sure his diabetes kit is in your carry-on with everything he will need for the duration of the trip, plus extra. Checked luggage gets lost and delayed. Security doesn't care about needles, I've flown a lot and no one has ever commented on it. Insulin is exempt from the 'liquid' rules.

Bring your own food/snacks... but really everyone should do this, the airlines don't provide anything edible.

You might want to make sure he is wearing a medic-alert bracelet or some type of ID identifying him as a diabetic.

www.tsa.gov/travelers/ai...ed-items.shtm