Hunt and Gather appeared in an article in TennisPro magazine (December 2010) by Rob Antoun about getting your clinics off to a good start. It combines the ABCs (agility, balance, coordination) with a healthy dose of competition. You will need some cones and clothes pins or other similar items. You should set this up before the players arrive.
Set up 15 cones in the back court (the area between the service line and the baseline). Hide 5 clothes pins under five random cones (one under each cone). Divide players into two teams, one at each sideline. Players take turns looking for the pins. They may only look one at a time per team, meaning two players (one from each team) will be looking simultaneously. They may only look under one cone at a time. Encourage quick, efficient movement. Each cone must stay in place after they look under it - no cheating by leaving it down or otherwise signalling it has already been searched. After their turn they return to the sideline and the next player goes. Game is over when all pins have been found.