Well, I'm in band too, but the only parade I've been in was the Christmas Parade (twice) and it was freezing then,but I do have practices out in the Florida heat and have halftime shows to do in wool longsleve uniforms, but on top of that I play flute, so I might not be much help.
Drink lots of water,and then go to the bathroom as close to the beginning as possible.
Take deep breaths if you're nervous
And if you have hair that covers your neck,see if you're allowed to tie it up, that helps alot.
And lastly, imagine you're in Alasaka...it works sometimes
Good Luck