We have called our field days "Just for the fun of it...Day." We've done a lot of cooperative things over the years.  Some of them include:

1. Water can relay - In this one, we divide the group (usually about 50 kids) into 9-10 groups. One of our teachers has a horse trough that she lets us use for this. We fill this with water. Each
   team has a tin can that we get from the cafeteria.  The only catch is that it has holes punched in the bottom of it. Each group is lined up one behind each other. The first kid in line takes the can and fills it with water and rushes back to the head of the line.  He then passes it over his head to the next person in line.  This continues until the can gets to the back of the line.  That person then runs to the other end of the area (usually 20 yards or so) and dumps what water is left in the can into a larger tin can (that we also got from the cafeteria).  The goal is to fill up their can with water.  The best part is at the end I get to give them all of their water back (that is I throw it all back on them!!)  It is an all time favorite.
2. Squirt Bottles Ready! - Everyone has a partner. The first partner has a water bottle (sports bottle, dish soap bottle...) and is blindfolded. The second partner stands behind the first, with their hands on the first partners shoulders. The partner behind is in control of turning the first partner when needed. The idea is for the partner in front to get directly in front of someone else (who is also blindfolded).  When they get into that position, the partner in back tells them to "squirt!" Since "turn about is fair play," we have the partners change places so the other partner now gets a chance to get wet...... I mean get someone else wet!
   
   We borrow some large water jugs from our high school as a "holding tank" for bottle refills.