Hi Bex,
I guess it depends on where you're going as things like the length of flight and type of country you're going to will make a difference to the things you need to think about.
I often fly to New Zealand so am used to long haul flights, and I just make sure I test regularly and take my insulin according to test results and what I've been served to eat. Do you carb count? If so, just continue to do that whenever you're served food on the plane. I often find my glucose levels go up a bit when I'm flying long haul, probably because you're very inactive during a long flight and you tend to eat more as they always seem to be handing out food! Be wary of taking food like fruit with you if you're travelling long haul - don't make the mistake I did and take an apple on the plane with you only to forget it's in your hand luggage, not declare it at the other end, and receive a NZ$200 fine for your troubles!
If you're on a short haul flight, your question of whether to take food with you or not will probably depend on whether the airline you're travelling with serves meals. Don't forget to take glucose with you though, or whatever you normally use for treating hypos.
I always take all my diabetic medication (insulin, blood test kit, etc) in my hand luggage just in case anything happens to my hold luggage - vital! If you're worried about carrying liquid (insulin) in your hand luggage, just tell the airport security staff before your bag goes through the x-ray machine that you have insulin in your bag and they will just wave you through. I've never had a problem with that, although the letter you've organised from the hospital will help if there are any problems.
Are you going to a hot climate? If so, don't forget that if you're out and about in the hot sun all day with your insulin in your bag that the heat will have a bad effect on your insulin and won't be as efficient as it would be if it was kept cool. I'd highly recommend you get one of those portable cooler bags (you can get ones specifically for your insulin pen) if you are travelling to somewhere hot. It took me ages during my first holiday in Greece to realise my glucose levels were so high because my insulin was in the sun all day!
I hope that's helped somewhat, but feel free to ask any more specific questions you might have. Have fun! :thumbup:
Erin