From Triathlete July 2011 issue.
Here is a sample warm-up that you can use on race day. Be sure to practice it prior to race day.
1. Arm-Swings and Stretching
2. 5 minutes of easy swimming
3. 3-4 sets of 20 strokes or drills that work best in open water:
Close-fisted freestyle: forces you to pull water with your forearms, not just your hands. Since you can’t feel your forearms in a wetsuit, it’s a good reminder of proper swim mechanics.
Kicking on your side: reminds you to rotate and glide along. Wetsuits tend to make athletes feel restrictive resulting in shorter, less efficient strokes.
After the drills do some pick-ups to engage your muscles in a race-specific range of motion and to increase blood flow.
[...] Perform your race day warm-up [...]