The heat could make you go higher or lower (I have a lot of hypo's in hot weather!) so make sure to keep an eye on your levels!
Your best bet would be simple carbs to give you a steady release, but honestly you can eat whatever you like as long as you're injecting properly for it!
Make sure to keep your insulin cool! And remember, watermelon has a very high glycaemic index (How fast it affects your levels), so if hypo you could treat yourself to a huge portion of that
Enjoy yourself and stay safe!
(P.S It might be a good idea to get yourself a medical ID bracelet/necklace or even set your phone background to a blank photo with In Case of Emergency information on)