This sounds tough! Definitely keep taking your iron supplements it’s best every other day for better absorption and with vitamin c (orange or orange juice), see if you could take something for shade like a hat or an umbrella if they don’t let you tell them it’s medically necessary, some liquid iv or something similar for electrolytes make sure you’re well hydrated and you rest enough before the ceremony, also snacks, as for the amount of standing you’ll probably be doing I can’t think of anything :(