Perhaps the most important aspect in endurance sports lasting more than about 1 hour, is the consumption of nutrition during the activity. This includes both the provision of electrolyte liquids and carbohydrates. Electrolytes will replace the missing salts that is lost in the sweat, while carbohydrates will help the body to produce the vital glycose that is needed to keep you going. It's important to have those supplies available with you while you race or train in the form of gels or other means (bottles, etc). A very good solution is to use a fuel belt!
Above: Wearing a 4 bottle fuel belt. This setup consists of 4 x 220ml bottles, two are in front and the other two on the back symmetrically placed. This belt also includes a mini pocket (on the back - not shown here) which can easily accommodate 3 GU size energy gels.
I am not the kind of person who is used to 'carry' staff while on the move, but this is a 'must' if you don't want your performance to drop. There are other alternative products available on the market too, but since top class Ironman athletes use Fuel Belt, why should we do differently? I recently purchased a 4 bottle belt and I have to say that I am more than relieved to know that I have a backup reserve available when I am out there pushing myself to complete a 2 or more hours of a triathlon session...
(here we see Ironman Champion Craig Alexander using Fuel Belt during his run. It's obvious that a proper nutrition plan is vital during an endurance sport such as triathlon)