I really appreciate this. The last convention I attended I was just dying in my armor cosplays and thick fabrics. I bought a mini fan off of Amazon to keep in my con bag after that.
There are miniature refrigeration units small enough to run off of a phone battery pack, about the size of a cell phone. The reviews say it can take a 12x12 room that is 90*F and cool it off to 55*F. And it will stay running for a few hours. If someone can figure out how to make the emissions safe for anime costumes, that would be awesome. You would just need more than one battery pack that is charged and possibly could stay cool all day.
Hey brother, TB/TK-41066 here! As you know it's real head to drink fluids before a troop because it's almost impossible to go to the bathroom in armor... Lol! Some good ideas.
Try tubing like an astronaut. I had a costume were it was hard to get to my face so i ran clean garden tubing from my mouth to my water bottle to drink. When I drank, the tube was next to my body and the water takes some heat with it and it was not bad to still drink/swallow. Just have a way to refill it if you run out.