I was watching IM new zealand or something like that on universalsports.com the other day. At the turn around, the pro athletes would grab a wristband or something that volunteers were handing off. Out of curiosity, what is it that they are getting? Some kind of nutrition?

Most likely, it was a lapped course (meaning the run consisted of multiple laps) Each time you completed a lap, you got a wristband. That way, both you, and the volunteers knew how far you were along the course. The one IM I have done (Vineman full) was like this