How to prevent feeling sick/passing out during long, hot parades for marching band?

I play with a samba drum band and I've seen too many people go down with heat stroke, especially when you've been playing a parade for hours in the heat. Best way to stop it is to plan ahead.

Drink lots of fluids - NOT alcohol or caffeine. Drink more than you would if you just walking around slowly. My favourite is coconut water (if you can get it - you can sometimes get it in tins), because it's a similar salt composition to blood, but water is good. Try and keep as cool as you can - you could try freezing your water bottle so that as it melts, it keeps everything else cool. Or why not try a camel pack on your back?

Keep in the shade as much as you can - wear a hat with a brim if you can. It isn't always possible I appreciate.

Avoid heavy clothing if possible - I know if you have a band uniform, again it isn't always possible (but you could suggest they have a light weight summer uniform?).

Keep something sugary with you - if you feel faint, it often gives you a lift.

If you're standing for long periods of time and you start feeling faint, but you can't go sit down, try wiggling your toes, and clenching the muscles in your calves and shins to force blood up to your head.

But most important - drink lots of fluid!!!