For the ladies out there going in August, I too will be there. I just recently bought these tank tops from Target, they are champion C9 and they are the dry-fit material around ($10). The back of them are all mesh as is the shoulder and the front is the dry-fit that wisk away moisture. I found them to be very cool and comfortable. Also you can't see your bra strap either.
Target also sells the same material shirts for men (around $10) and boys (not quite $10, I think $7 or $8), got both for dh and ds by Champion C9.
They don't make them for girls, not quite sure why, dd would really like them.
You can get similiar shirts by Nike for like $25/30 and Dicks has their own brand, but they still cost more than the C9 shirts at Target.
They make shorts too, but I didn't get those.