Stretching? I did a sprint triathlon yesterday and i forgot to stretch before the start... After coming back in from the bike portion, my calves started to cramp up on the run about 30 seconds after leaving the transition area. I had to stop for a minute to relax and stretch them out before getting back to running. I was perfectly fine after that.

[water/nutrition wasn't an issue since i made sure to eat/drink enough before the start and while on the bike and i never had cramps during my training either]