A relay race for a hot day!
Fill four buckets with water and place them about 10 feet apart in a straight line. Put a t-shirt in each.
Divide the group into four teams, and have each team line up across from a bucket, about 30 feet away.
Once the race begins, the first member runs to the bucket, puts on the wet t-shirt, and runs back to his/her team. When he/she reaches the team, he/she removes the shirt and gives it to the next person.
The next person runs with the shirt in their hand to the bucket, dunks the shirt into the water, and puts on the wet shirt, and so this continues until you are back to the first team member.
The first team to have all players finish the task wins!